Evaluate Trig Sub Homework: Int from Infty to -Infty

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In summary, the conversation discusses the process of evaluating the integral \int_{\infty}^{-\infty} \frac{dz}{(z^2+x^2)^(3/2)} using trigonometric substitution. The final answer is found to be \frac{L}{x^2 \sqrt(L^2+x^2)} when the bounds are L to -L. There is also a question about the process used in the book to get the answer \frac{z}{x^2\sqrt(z^2+x^2)} with bounds from infinity to -infinity, which is later resolved.
  • #1
Winzer
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Homework Statement


Having trouble evaluating:
[tex]\int_{\infty}^{-\infty} \frac{dz}{(z^2+x^2)^(3/2)}[/tex]

Homework Equations


Trig sub
[tex] z=xtan(\theta)[/tex]

The Attempt at a Solution


comes down to:
[tex]\int_{x\frac{\pi}{2}}^{-x\frac{\pi}{2}} cos(\theta) d\theta [/tex]
goes to
[tex] sin(\theta)[/tex] from [tex]x\frac{\pi}{2} \longrightarrow -x\frac{\pi}{2}[/tex]
ehh!?
 
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  • #2
You can change the bounds differently. Think about it, as long x is some constant, and z approaching negative infinity and positive infinity, the tan theta has to be...
 
  • #3
mm...just [tex]\frac{\pi}{2}[/tex]
 
  • #4
is that supposed to be to the 3/2 power or is that a constant multiplying the denominator?
 
  • #5
rocophysics said:
is that supposed to be to the 3/2 power or is that a constant multiplying the denominator?
Sorry it is that quantity raised to the (3/2)
 
  • #6
Basically I am trying to figure out how this book got
[tex] \frac{z}{x^2\sqrt(z^2+x^2)}[/tex] with bounds from infinity to -infinity.
They then go on to get [1--1]=2.

I have to do this for a similar problem except my bounds will be L to -L.
the answer is: [tex] \frac{L}{x^2 \sqrt(L^2+x^2)}[/tex] I do not know how.
Trying to remember how to do bounds on trig subs.
 
  • #7
Anyone?
 
  • #8
Winzer said:
Basically I am trying to figure out how this book got
[tex] \frac{z}{x^2\sqrt(z^2+x^2)}[/tex] with bounds from infinity to -infinity.
They then go on to get [1--1]=2.

I have to do this for a similar problem except my bounds will be L to -L.
the answer is: [tex] \frac{L}{x^2 \sqrt(L^2+x^2)}[/tex] I do not know how.
Trying to remember how to do bounds on trig subs.

maybe divide top and bottom by z. then plug in the limits from infinity to -infinity

I get zero? I get (1/x^2)-(1/X^2)
 
  • #9
Winzer said:
Basically I am trying to figure out how this book got
[tex] \frac{z}{x^2\sqrt(z^2+x^2)}[/tex] with bounds from infinity to -infinity.
They then go on to get [1--1]=2.

I have to do this for a similar problem except my bounds will be L to -L.
the answer is: [tex] \frac{L}{x^2 \sqrt(L^2+x^2)}[/tex] I do not know how.
Trying to remember how to do bounds on trig subs.

Integrating with respect to z or x? State the exact question given to you please.
 

What is "Evaluate Trig Sub Homework: Int from Infty to -Infty"?

"Evaluate Trig Sub Homework: Int from Infty to -Infty" is a type of mathematical problem that involves finding the integral (area under the curve) of a function that has been transformed using trigonometric substitutions. The problem typically involves finding the integral over an infinite range, from positive infinity to negative infinity.

Why is "Evaluate Trig Sub Homework: Int from Infty to -Infty" important?

This type of problem is important because it allows us to solve integrals that cannot be solved using traditional methods. Trigonometric substitutions can be used to transform complex integrals into simpler ones, making it easier to find the solution.

What are the steps to solving "Evaluate Trig Sub Homework: Int from Infty to -Infty"?

The first step is to identify if the problem requires a trigonometric substitution. Then, use the appropriate substitution to transform the integral. Next, evaluate the integral using techniques such as integration by parts or partial fractions. Finally, take the limits of the integral to find the final solution.

What are some common trigonometric substitutions used in "Evaluate Trig Sub Homework: Int from Infty to -Infty"?

Some common substitutions include u = tan(x/2), u = sin(x), and u = cos(x). These substitutions can be used to transform integrals involving trigonometric functions such as sine, cosine, and tangent.

Can "Evaluate Trig Sub Homework: Int from Infty to -Infty" be solved using a calculator?

Yes, a calculator can be used to evaluate the final integral. However, the trigonometric substitution and any additional algebraic manipulations must be done by hand. It is important to note that some calculators may not be able to handle extremely large or small values, which can be a limitation when solving these types of problems.

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