With 15 exponential equations. Power or exponential equations. you can get acquainted with functions and derivatives

Solution of exponential equations. Examples.

Attention!
There are additional
material in Special Section 555.
For those who strongly "not very..."
And for those who "very much...")

What's happened exponential equation? This is an equation in which the unknowns (x) and expressions with them are in indicators some degrees. And only there! It is important.

There you are examples of exponential equations:

3 x 2 x = 8 x + 3

Note! In the bases of degrees (below) - only numbers. V indicators degrees (above) - a wide variety of expressions with x. If, suddenly, an x appears in the equation somewhere other than the indicator, for example:

this will be a mixed type equation. Such equations do not have clear rules for solving. We will not consider them for now. Here we will deal with solution of exponential equations in its purest form.

In fact, even pure exponential equations are not always clearly solved. But there are certain types of exponential equations that can and should be solved. These are the types we'll be looking at.

Solution of the simplest exponential equations.

Let's start with something very basic. For instance:

Even without any theory, by simple selection it is clear that x = 2. Nothing more, right!? No other x value rolls. And now let's look at the solution of this tricky exponential equation:

What have we done? We, in fact, just threw out the same bottoms (triples). Completely thrown out. And, what pleases, hit the mark!

Indeed, if in the exponential equation on the left and on the right are the same numbers in any degree, these numbers can be removed and equal exponents. Mathematics allows. It remains to solve a much simpler equation. It's good, right?)

However, let's remember ironically: you can remove the bases only when the base numbers on the left and right are in splendid isolation! Without any neighbors and coefficients. Let's say in the equations:

2 x +2 x + 1 = 2 3 , or

You can't remove doubles!

Well, we have mastered the most important thing. How to move from evil exponential expressions to simpler equations.

"Here are those times!" - you say. "Who will give such a primitive on the control and exams!?"

Forced to agree. Nobody will. But now you know where to go when solving confusing examples. It is necessary to bring it to mind, when the same base number is on the left - on the right. Then everything will be easier. Actually, this is the classics of mathematics. We take the original example and transform it to the desired US mind. According to the rules of mathematics, of course.

Consider examples that require some additional effort to bring them to the simplest. Let's call them simple exponential equations.

Solution of simple exponential equations. Examples.

When solving exponential equations, the main rules are actions with powers. Without knowledge of these actions, nothing will work.

To actions with degrees, one must add personal observation and ingenuity. Do we need the same base numbers? So we are looking for them in the example in an explicit or encrypted form.

Let's see how this is done in practice?

Let's give us an example:

2 2x - 8 x+1 = 0

First glance at grounds. They... They are different! Two and eight. But it's too early to be discouraged. It's time to remember that

Two and eight are relatives in degree.) It is quite possible to write down:

8 x+1 = (2 3) x+1

If we recall the formula from actions with powers:

(a n) m = a nm ,

it generally works great:

8 x+1 = (2 3) x+1 = 2 3(x+1)

The original example looks like this:

2 2x - 2 3(x+1) = 0

We transfer 2 3 (x+1) to the right (no one canceled the elementary actions of mathematics!), we get:

2 2x \u003d 2 3 (x + 1)

That's practically all. Removing bases:

We solve this monster and get

This is the correct answer.

In this example, knowing the powers of two helped us out. We identified in the eight, the encrypted deuce. This technique (encoding common bases under different numbers) is a very popular trick in exponential equations! Yes, even in logarithms. One must be able to recognize the powers of other numbers in numbers. This is extremely important for solving exponential equations.

The fact is that raising any number to any power is not a problem. Multiply, even on a piece of paper, and that's all. For example, everyone can raise 3 to the fifth power. 243 will turn out if you know the multiplication table.) But in exponential equations, much more often it is necessary not to raise to a power, but vice versa ... what number to what extent hides behind the number 243, or, say, 343... No calculator will help you here.

You need to know the powers of some numbers by sight, yes ... Shall we practice?

Determine what powers and what numbers are numbers:

2; 8; 16; 27; 32; 64; 81; 100; 125; 128; 216; 243; 256; 343; 512; 625; 729, 1024.

Answers (in a mess, of course!):

5 4 ; 2 10 ; 7 3 ; 3 5 ; 2 7 ; 10 2 ; 2 6 ; 3 3 ; 2 3 ; 2 1 ; 3 6 ; 2 9 ; 2 8 ; 6 3 ; 5 3 ; 3 4 ; 2 5 ; 4 4 ; 4 2 ; 2 3 ; 9 3 ; 4 5 ; 8 2 ; 4 3 ; 8 3 .

If you look closely, you can see a strange fact. There are more answers than questions! Well, it happens... For example, 2 6 , 4 3 , 8 2 is all 64.

Let's assume that you have taken note of the information about acquaintance with numbers.) Let me remind you that for solving exponential equations, we apply the whole stock of mathematical knowledge. Including from the lower-middle classes. You didn't go straight to high school, did you?

For example, when solving exponential equations, putting the common factor out of brackets very often helps (hello to grade 7!). Let's see an example:

3 2x+4 -11 9 x = 210

And again, the first look - on the grounds! The bases of the degrees are different ... Three and nine. And we want them to be the same. Well, in this case, the desire is quite feasible!) Because:

9 x = (3 2) x = 3 2x

According to the same rules for actions with degrees:

3 2x+4 = 3 2x 3 4

That's great, you can write:

3 2x 3 4 - 11 3 2x = 210

We gave an example for the same reasons. So, what is next!? Threes cannot be thrown out ... Dead end?

Not at all. Remembering the most universal and powerful decision rule all math tasks:

If you don't know what to do, do what you can!

You look, everything is formed).

What is in this exponential equation can do? Yes, the left side directly asks for parentheses! The common factor of 3 2x clearly hints at this. Let's try, and then we'll see:

3 2x (3 4 - 11) = 210

3 4 - 11 = 81 - 11 = 70

The example keeps getting better and better!

We recall that in order to eliminate bases, we need a pure degree, without any coefficients. The number 70 bothers us. So we divide both sides of the equation by 70, we get:

Op-pa! Everything has been fine!

This is the final answer.

It happens, however, that taxiing out on the same grounds is obtained, but their liquidation is not. This happens in exponential equations of another type. Let's get this type.

Change of variable in solving exponential equations. Examples.

Let's solve the equation:

4 x - 3 2 x +2 = 0

First - as usual. Let's move on to the base. To the deuce.

4 x = (2 2) x = 2 2x

We get the equation:

2 2x - 3 2 x +2 = 0

And here we'll hang. The previous tricks will not work, no matter how you turn it. We'll have to get from the arsenal of another powerful and versatile way. It's called variable substitution.

The essence of the method is surprisingly simple. Instead of one complex icon (in our case, 2 x), we write another, simpler one (for example, t). Such a seemingly meaningless replacement leads to amazing results!) Everything just becomes clear and understandable!

So let

Then 2 2x \u003d 2 x2 \u003d (2 x) 2 \u003d t 2

We replace in our equation all powers with x's by t:

Well, it dawns?) Haven't forgotten quadratic equations yet? We solve through the discriminant, we get:

Here, the main thing is not to stop, as it happens ... This is not the answer yet, we need x, not t. We return to Xs, i.e. making a replacement. First for t 1:

That is,

One root was found. We are looking for the second one, from t 2:

Um... Left 2 x, Right 1... A hitch? Yes, not at all! It is enough to remember (from actions with degrees, yes ...) that a unity is any number to zero. Any. Whatever you need, we will put it. We need a two. Means:

Now that's all. Got 2 roots:

This is the answer.

At solving exponential equations at the end, some awkward expression is sometimes obtained. Type:

From the seven, a deuce through a simple degree does not work. They are not relatives ... How can I be here? Someone may be confused ... But the person who read on this site the topic "What is a logarithm?" , only smile sparingly and write down with a firm hand the absolutely correct answer:

There can be no such answer in tasks "B" on the exam. There is a specific number required. But in tasks "C" - easily.

This lesson provides examples of solving the most common exponential equations. Let's highlight the main one.

Practical Tips:

1. First of all, we look at grounds degrees. Let's see if they can't be done the same. Let's try to do this by actively using actions with powers. Do not forget that numbers without x can also be turned into degrees!

2. We try to bring the exponential equation to the form when the left and right are the same numbers to any degree. We use actions with powers and factorization. What can be counted in numbers - we count.

3. If the second advice did not work, we try to apply the variable substitution. The result can be an equation that is easily solved. Most often - square. Or fractional, which also reduces to a square.

4. To successfully solve exponential equations, you need to know the degrees of some numbers "by sight".

As usual, at the end of the lesson you are invited to solve a little.) On your own. From simple to complex.

Solve exponential equations:

More difficult:

2 x + 3 - 2 x + 2 - 2 x \u003d 48

9 x - 8 3 x = 9

2 x - 2 0.5 x + 1 - 8 = 0

Find product of roots:

2 3-x + 2 x = 9

Happened?

Well, then the most complicated example (it is solved, however, in the mind ...):

7 0.13x + 13 0.7x+1 + 2 0.5x+1 = -3

What is more interesting? Then here's a bad example for you. Quite pulling on increased difficulty. I will hint that in this example, ingenuity and the most universal rule for solving all mathematical tasks saves.)

2 5x-1 3 3x-1 5 2x-1 = 720 x

An example is simpler, for relaxation):

9 2 x - 4 3 x = 0

And for dessert. Find the sum of the roots of the equation:

x 3 x - 9x + 7 3 x - 63 = 0

Yes Yes! This is a mixed type equation! Which we did not consider in this lesson. And what to consider them, they need to be solved!) This lesson is quite enough to solve the equation. Well, ingenuity is needed ... And yes, the seventh grade will help you (this is a hint!).

Answers (in disarray, separated by semicolons):

one; 2; 3; 4; there are no solutions; 2; -2; -5; 4; 0.

Is everything successful? Fine.

There is a problem? No problem! In Special Section 555, all these exponential equations are solved with detailed explanations. What, why, and why. And, of course, there is additional valuable information on working with all sorts of exponential equations. Not only with these.)

One last fun question to consider. In this lesson, we worked with exponential equations. Why didn't I say a word about ODZ here? In equations, this is a very important thing, by the way ...

If you like this site...

By the way, I have a couple more interesting sites for you.)

You can practice solving examples and find out your level. Testing with instant verification. Learning - with interest!)

you can get acquainted with functions and derivatives.

At the stage of preparation for the final testing, high school students need to improve their knowledge on the topic "Exponential Equations". The experience of past years indicates that such tasks cause certain difficulties for schoolchildren. Therefore, high school students, regardless of their level of preparation, need to carefully master the theory, memorize the formulas and understand the principle of solving such equations. Having learned to cope with this type of tasks, graduates will be able to count on high scores when passing the exam in mathematics.

Get ready for the exam testing together with Shkolkovo!

When repeating the materials covered, many students are faced with the problem of finding the formulas needed to solve the equations. A school textbook is not always at hand, and the selection of the necessary information on a topic on the Internet takes a long time.

The Shkolkovo educational portal invites students to use our knowledge base. We are implementing a completely new method of preparing for the final test. Studying on our site, you will be able to identify gaps in knowledge and pay attention to precisely those tasks that cause the greatest difficulties.

Teachers of "Shkolkovo" collected, systematized and presented all the material necessary for the successful passing of the exam in the most simple and accessible form.

The main definitions and formulas are presented in the "Theoretical Reference" section.

For a better assimilation of the material, we recommend that you practice the assignments. Carefully review the examples of exponential equations with solutions presented on this page in order to understand the calculation algorithm. After that, proceed with the tasks in the "Catalogs" section. You can start with the easiest tasks or go straight to solving complex exponential equations with several unknowns or . The database of exercises on our website is constantly supplemented and updated.

Those examples with indicators that caused you difficulties can be added to the "Favorites". So you can quickly find them and discuss the solution with the teacher.

To successfully pass the exam, study on the Shkolkovo portal every day!

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Attention! The slide preview is for informational purposes only and may not represent the full extent of the presentation. If you are interested in this work, please download the full version.

Lesson type

: a lesson on the generalization and complex application of knowledge, skills and abilities on the topic “Exponential equations and ways to solve them”.

Lesson goals.

Tutorials:
repeat and systematize the main material of the topic “Exponential equations, their solutions”; consolidate the ability to use appropriate algorithms when solving exponential equations of various types; preparation for the exam.
Developing:
develop logical and associative thinking of students; to promote the development of the skill of independent application of knowledge.
Educational:
to cultivate purposefulness, attention and accuracy in solving equations.

Equipment:

computer and multimedia projector.

The lesson uses Information Technology : methodological support for the lesson - presentation in Microsoft Power Point.

During the classes

Every skill comes with hard work.

I. Setting the goal of the lesson(slide number 2 )

In this lesson, we will summarize and generalize the topic “Exponential Equations, Their Solutions”. Let's get acquainted with the typical tasks of the exam of different years on this topic.

Tasks for solving exponential equations can be found in any part of the USE tasks. In the part " V " usually propose to solve the simplest exponential equations. In the part " WITH " you can meet more complex exponential equations, the solution of which is usually one of the stages of the task.

For instance ( slide number 3 ).

USE - 2007

B 4 - Find the largest value of the expression x y, where ( X; at) is the solution of the system:

USE - 2008

B 1 - Solve Equations:

a) X 6 3X – 36 6 3X = 0;

b) 4 X +1 + 8 4X= 3.

USE - 2009

B 4 - Find the value of the expression x + y, where ( X; at) is the solution of the system:

USE - 2010

– Solve the equation: 7 X– 2 = 49. – Find the roots of the equation: 4 X 2 + 3X – 2 - 0,5 2x2 + 2X – 1 = 0. – Solve the system of equations:

II. Updating of basic knowledge. Repetition

(Slides #4 – 6 class presentations)

The screen is shown reference summary of theoretical material on this topic.

The following questions are discussed:

What equations are called indicative?
Name the main ways to solve them. Give examples of their types ( slide number 4 )

(Self-solve the proposed equations for each method and perform a self-test using the slide)

What theorem is used to solve the simplest exponential equations of the form: and f(x) = a g(x) ?
What other methods for solving exponential equations exist? ( slide number 5 )

Factorization method

Reception of division (multiplication) by an exponential expression other than zero, when solving homogeneous exponential equations

Advice:

when solving exponential equations, it is useful to first make transformations, obtaining degrees with the same bases in both parts of the equation.

Solving equations with the last two methods followed by comments

(slide number 6 ).

. 4 X+ 1 – 2 4 X– 2 = 124, 4 X– 2 (4 3 - 2) = 124, 4 X– 2 62 = 124,

4 X– 2 = 2, 4 X– 2 = 4 0,5 , X– 2 = 0,5, x = 2,5 .

2 2 2x – 3 2 X 5X - 5 5 2X= 0¦: 5 2 X 0,

2 (2/5) 2x - 3 (2/5) X - 5 = 0,

t = (2/5) x, t > 0, 2t 2 - 3t- 5 = 0,t= -1(?...), t = 5/2; 5/2 = (2/5) x, X= ?...

III. Solving USE tasks 2010

Students independently solve the tasks proposed at the beginning of the lesson on slide No. 3, using the instructions for the solution, check their decision process and answers to them using the presentation ( slide number 7). In the process of work, options and methods for solving are discussed, attention is drawn to possible errors in the solution.

: a) 7 X– 2 = 49, b) (1/6) 12 - 7 x = 36. Answer: a) X= 4, b) X = 2. : 4 X 2 + 3X – 2 - 0,5 2x2 + 2X- 1 \u003d 0. (You can replace 0.5 \u003d 4 - 0.5)

Solution. ,

X 2 + 3X – 2 = -X 2 - 4X + 0,5 …

Answer: X= -5/2, X = 1/2.

: 5 5 tg y+ 4 = 5 -tg y, at cos y< 0.

Suggestion for a decision

. 5 5 tg y+ 4 = 5 -tg y¦ 5 tg y 0,

5 5 2g y+ 4 5 tg y- 1 = 0. Let X= 5 tg y , …

5 tg y = -1 (?...), 5 tg y= 1/5.

Since tg y= -1 and cos y< 0, then at II coordinate quarter

Answer: at= 3/4 + 2k, k N.

IV. Whiteboard Collaboration

The task of a high level of learning is considered - slide number 8. With the help of this slide, there is a dialogue between the teacher and students, which contributes to the development of the solution.

- At what parameter a equation 2 2 X – 3 2 X + a 2 – 4a= 0 has two roots?

Let t= 2 X, where t > 0 . We get t 2 – 3t + (a 2 – 4a) = 0 .

one). Since the equation has two roots, then D > 0;

2). Because t 1,2 > 0, then t 1 t 2 > 0, that is a 2 – 4a> 0 (?...).

Answer: a(– 0.5; 0) or (4; 4.5).

V. Verification work

(slide number 9 )

Students perform verification work on leaflets, exercising self-control and self-assessment of the work performed with the help of a presentation, asserting itself in the topic. They independently determine for themselves a program for regulating and correcting knowledge based on mistakes made in workbooks. Sheets with completed independent work are handed over to the teacher for verification.

The underlined numbers are basic, those with an asterisk are advanced.

Solution and answers.

0,3 2X + 1 = 0,3 – 2 , 2X + 1 = -2, X= -1,5.

(1; 1).

3. 2 X– 1 (5 2 4 - 4) = 19, 2 X– 1 76 = 19, 2 X– 1 = 1/4, 2 X– 1 = 2 – 2 , X– 1 = -2,

x = -1.

4 *.3 9 x = 2 3 X 5X+ 5 25 X | : 25 X ,

3 (9/25) x = 2 (3/5) X+ 5,

3 (9/27) X = 2 (3/5) X + 5 = 0,

3 (3/5) 2X – 2 (3/5) X - 5 = 0,…, (3/5) X = -1 (not suitable),

(3/5) X = 5, x = -1.

VI. Homework
(slide number 10 )

Repeat § 11, 12.
From the materials of the Unified State Exam 2008 - 2010, select tasks on the topic and solve them.

Home test work

Do not be afraid of my words, you have already encountered this method in the 7th grade when you studied polynomials.

For example, if you needed:

Let's group: the first and third terms, as well as the second and fourth.

It is clear that the first and third are the difference of the squares:

and the second and fourth have a common factor of three:

Then the original expression is equivalent to this:

Where to take out the common factor is no longer difficult:

Hence,

This is approximately how we will act when solving exponential equations: look for "commonality" among the terms and take it out of the brackets, well, then - come what may, I believe that we will be lucky =))

Example #14

On the right is far from a power of seven (I checked!) And on the left - a little better ...

You can, of course, “chop off” the factor a from the second term from the first term, and then deal with what you have received, but let's act more prudently with you.

I don't want to deal with the fractions that are inevitably produced by "selection", so shouldn't I be better off enduring?

Then I won’t have fractions: as they say, both the wolves are full and the sheep are safe:

Count the expression in brackets.

Magically, magically, it turns out that (surprisingly, although what else can we expect?).

Then we reduce both sides of the equation by this factor. We get: where.

Here is a more complicated example (quite a bit, really):

Here's the trouble! We have no common ground here!

It's not entirely clear what to do now.

And let's do what we can: firstly, we will move the “fours” in one direction, and the “fives” in the other:

Now let's take out the "common" on the left and right:

So what now?

What is the benefit of such a stupid grouping? At first glance, it is not visible at all, but let's look deeper:

Well, now let's make it so that on the left we have only the expression c, and on the right - everything else.

How can we do it?

And here's how: Divide both sides of the equation first by (so we get rid of the exponent on the right), and then divide both sides by (so we get rid of the numerical factor on the left).

Finally we get:

Incredible!

On the left we have an expression, and on the right - just.

Then we immediately conclude that

Example #15

I will give his brief solution (not really bothering to explain), try to figure out all the “subtleties” of the solution yourself.

Now the final consolidation of the material covered.

Independently solve the following 7 tasks (with answers)

Let's take the common factor out of brackets:
We represent the first expression in the form: , divide both parts by and get that
, then the original equation is converted to the form: Well, now a hint - look for where you and I have already solved this equation!
Imagine how, how, ah, well, then divide both parts by, so you get the simplest exponential equation.
Take it out of brackets.
Take it out of brackets.

EXPOSITIONAL EQUATIONS. AVERAGE LEVEL

I assume that after reading the first article, which told what are exponential equations and how to solve them, you have mastered the necessary minimum of knowledge needed to solve the simplest examples.

Now I will analyze another method for solving exponential equations, this is ...

Method for introducing a new variable (or substitution)

He solves most of the "difficult" problems, on the topic of exponential equations (and not only equations).

This method is one of most commonly used in practice. First, I recommend that you familiarize yourself with the topic.

As you already understood from the name, the essence of this method is to introduce such a change of variable that your exponential equation will miraculously transform into one that you can already easily solve.

All that remains for you after solving this very “simplified equation” is to make a “reverse replacement”: that is, to return from the replaced to the replaced.

Let's illustrate what we just said with a very simple example:

Example 16. Simple replacement method

This equation is solved with "simple substitution", as mathematicians call it disparagingly.

Indeed, the substitution here is the most obvious. It just needs to be seen that

Then the original equation becomes:

If we additionally imagine how, then it is quite clear that it is necessary to replace ...

Of course, .

What then becomes the original equation? And here's what:

You can easily find its roots on your own:.

What should we do now?

It's time to return to the original variable.

What did I forget to include?

Namely: when replacing a certain degree with a new variable (that is, when replacing a type), I will be interested in only positive roots!

You yourself can easily answer why.

Thus, we are not interested in you, but the second root is quite suitable for us:

Then where.

Answer:

As you can see, in the previous example, the replacement was asking for our hands. Unfortunately, this is not always the case.

However, let's not go straight to the sad, but practice on one more example with a fairly simple replacement

Example 17. Simple replacement method

It is clear that most likely it will be necessary to replace (this is the smallest of the powers included in our equation).

However, before introducing a replacement, our equation needs to be “prepared” for it, namely: , .

Then you can replace, as a result I will get the following expression:

Oh horror: a cubic equation with absolutely terrible formulas for its solution (well, speaking in general terms).

But let's not immediately despair, but think about what we should do.

I'll suggest cheating: we know that in order to get a "beautiful" answer, we need to get in the form of some power of three (why would that be, huh?).

And let's try to guess at least one root of our equation (I'll start guessing from the powers of three).

First guess. Is not a root. Alas and ah...

.
The left side is equal.
Right part: !

There is! Guessed the first root. Now things will get easier!

Do you know about the "corner" division scheme? Of course you know, you use it when you divide one number by another.

But few people know that the same can be done with polynomials.

There is one wonderful theorem:

Applicable to my situation it tells me what is divisible without a remainder by.

How is division carried out? That's how:

I look at which monomial I should multiply to get

It is clear that on, then:

I subtract the resulting expression from, I get:

Now, what do I need to multiply to get?

It is clear that on, then I will get:

and again subtract the resulting expression from the remaining one:

Well, the last step, I multiply by, and subtract from the remaining expression:

Hooray, the division is over! What have we accumulated in private?

By itself: .

Then we got the following expansion of the original polynomial:

Let's solve the second equation:

It has roots:

Then the original equation:

has three roots:

We, of course, discard the last root, since it is less than zero.

And the first two after the reverse replacement will give us two roots:

Answer: ..

I didn't mean to scare you with this example!

Rather, on the contrary, I set out to show that although we had a fairly simple replacement, nevertheless, it led to a rather complex equation, the solution of which required some special skills from us.

Well, no one is immune from this. But the change in this case was pretty obvious.

Example #18 (with a less obvious substitution)

It is not at all clear what we should do: the problem is that in our equation there are two different bases and one base cannot be obtained from the other by raising it to any (reasonable, naturally) power.

However, what do we see?

Both bases differ only in sign, and their product is the difference of squares equal to one:

Definition:

Thus, the numbers that are bases in our example are conjugate.

In that case, the smart move would be multiply both sides of the equation by the conjugate number.

For example, on, then the left side of the equation will become equal, and the right side.

If we make a replacement, then our original equation with you will become like this:

its roots, then, but remembering that, we get that.

Answer: , .

As a rule, the replacement method is enough to solve most of the "school" exponential equations.

The following tasks of an increased level of complexity are taken from the exam options.

Three tasks of increased complexity from the exam options

You are already literate enough to solve these examples on your own. I will only give the required replacement.

Solve the equation:
Find the roots of the equation:
Solve the equation: . Find all the roots of this equation that belong to the segment:

Now for some quick explanations and answers:

Example #19

Here it suffices to note that and.

Then the original equation will be equivalent to this:

This equation is solved by replacing

Do the following calculations yourself.

In the end, your task will be reduced to solving the simplest trigonometric (depending on the sine or cosine). We will discuss the solution of such examples in other sections.

Example #20

Here you can even do without replacement ...

It is enough to move the subtrahend to the right and present both bases through powers of two: and then immediately go to the quadratic equation.

Example #21

It is also solved quite standardly: imagine how.

Then, replacing we get a quadratic equation: then,

Do you already know what a logarithm is? Not? Then urgently read the topic!

The first root, obviously, does not belong to the segment, and the second is incomprehensible!

But we will find out very soon!

Since, then (this is a property of the logarithm!)

Subtract from both parts, then we get:

The left side can be represented as:

multiply both sides by:

can be multiplied by, then

Then let's compare:

since then:

Then the second root belongs to the desired interval

Answer:

As you see, the selection of the roots of exponential equations requires a fairly deep knowledge of the properties of logarithms, so I advise you to be as careful as possible when solving exponential equations.

As you know, in mathematics everything is interconnected!

As my math teacher used to say: "You can't read math like history overnight."

As a rule, all the difficulty in solving problems of an increased level of complexity is precisely the selection of the roots of the equation.

Another practice example...

Example 22

It is clear that the equation itself is solved quite simply.

Having made the substitution, we reduce our original equation to the following:

First, let's consider first root.

Compare and: since, then. (property of the logarithmic function, at).

Then it is clear that the first root does not belong to our interval either.

Now the second root: . It is clear that (since the function is increasing).

It remains to compare and

since, then, at the same time.

Thus, I can "drive a peg" between and.

This peg is a number.

The first expression is less than and the second is greater than.

Then the second expression is greater than the first and the root belongs to the interval.

Answer: .

In conclusion, let's look at another example of an equation where the replacement is rather non-standard.

Example #23 (An equation with a non-standard replacement!)

Let's start right away with what you can do, and what - in principle, you can, but it's better not to do it.

It is possible - to represent everything through the powers of three, two and six.

Where it leads?

Yes, and will not lead to anything: a hodgepodge of degrees, some of which will be quite difficult to get rid of.

What then is needed?

Let's note that a

And what will it give us?

And the fact that we can reduce the solution of this example to the solution of a fairly simple exponential equation!

First, let's rewrite our equation as:

Now we divide both sides of the resulting equation into:

Eureka! Now we can replace, we get:

Well, now it's your turn to solve problems for demonstration, and I will give only brief comments to them so that you do not go astray! Good luck!

Example #24

The most difficult!

Seeing a replacement here is oh, how ugly! Nevertheless, this example can be completely solved using selection of a full square.

To solve it, it suffices to note that:

So here's your replacement:

(Note that here, with our replacement, we cannot discard the negative root!!! And why, what do you think?)

Now, to solve the example, you have to solve two equations:

Both of them are solved by the "standard replacement" (but the second one in one example!)

Example #25

2. Notice that and make a substitution.

Example #26

3. Expand the number into coprime factors and simplify the resulting expression.

Example #27

4. Divide the numerator and denominator of the fraction by (or if you prefer) and make the substitution or.

Example #28

5. Note that the numbers and are conjugate.

SOLUTION OF EXPONENTIAL EQUATIONS BY THE METHOD OF LOGARIFMING. ADVANCED LEVEL

In addition, let's look at another way - solution of exponential equations by the logarithm method.

I cannot say that the solution of exponential equations by this method is very popular, but in some cases only it can lead us to the correct solution of our equation.

Especially often it is used to solve the so-called " mixed equations': that is, those where there are functions of different types.

Example #29

in the general case, it can only be solved by taking the logarithm of both parts (for example, by base), in which the original equation turns into the following:

Let's consider the following example:

It is clear that we are only interested in the ODZ of the logarithmic function.

However, this follows not only from the ODZ of the logarithm, but for another reason.

I think that it will not be difficult for you to guess which one.

Let's take the logarithm of both sides of our equation to the base:

As you can see, taking the logarithm of our original equation quickly led us to the correct (and beautiful!) answer.

Let's practice with one more example.