Inverse Substitution: Solving for z in Terms of x

In summary, to put z back in terms of x after making the inverse substitution x=2tan(z), you can use the Pythagorean theorem to find the hypotenuse of a right triangle with opposite side x and adjacent side 2. Then, sin(z) can be expressed as 4x/sqrt(x^2+4). This method is helpful in avoiding memorization and deriving the solution.
  • #1
jumbogala
423
4

Homework Statement


Let's say you make the inverse substitution x = 2tan(z) in some integral.

Let's say you evaluate the integral get something like like 4sin(z). How do you put z back in terms of x?

Homework Equations





The Attempt at a Solution


I can do it by saying arctan(x/2) = z, but my teacher said we are not allowed to state the answer that way. I'm not sure how else you would do that...?
 
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  • #2
Draw a right triangle where tan(x)=x/2. For example, let the side opposite the angle z be x and the side adjacent be 2. Now use Pythagoras to find the hypotenuse. What then is sin(z) in terms of x? It's opposite over hypotenuse, right?
 
  • #3
Ohh okay, so in this case you would end up with 4x / sqrt(x^2 + 4).

Thanks!
 
  • #4
Exactly. 4*sin(arctan(x/2))=4x/sqrt(x^2+4). Drawing a triangle is nice way to derive stuff like that without memorizing it.
 

Related to Inverse Substitution: Solving for z in Terms of x

1. What is inverse substitution?

Inverse substitution is a mathematical technique used to solve equations that involve multiple variables. It involves isolating one variable in an equation and substituting it into another equation to eliminate that variable and solve for the remaining variables.

2. When do you use inverse substitution?

Inverse substitution is typically used when solving systems of equations, where there are multiple equations that need to be solved simultaneously. It is also commonly used in calculus to solve integrals.

3. How do you perform inverse substitution?

To perform inverse substitution, you first need to identify one variable that you want to eliminate from the equations. Then, you solve for that variable in one of the equations and substitute it into the other equations. This eliminates the variable and allows you to solve for the remaining variables.

4. What are the benefits of using inverse substitution?

Inverse substitution allows you to solve systems of equations in a systematic and efficient way. It also helps to simplify complicated equations and makes them easier to solve. Additionally, it is a useful technique in calculus to solve integrals.

5. What are some common mistakes when using inverse substitution?

One common mistake is not isolating the variable properly before substitution, which can lead to incorrect solutions. Another mistake is substituting the wrong value for the eliminated variable, which can also result in incorrect solutions. It is important to carefully follow the steps of inverse substitution to avoid these mistakes.

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