How to Prove the Integral of sin^7 x/(1+x^10) dx from -pi/2 to pi/2 is 0?

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In summary, the integral of sin^7 x/(1+x^10) dx from -pi/2 to pi/2 is 0, as the integrand is the product of an odd function (sin^7 x) and an even function (1/(1+x^10)), resulting in an overall odd function that integrates to 0 due to symmetry.
  • #1
Math9999

Homework Statement


Find the integral of sin^7 x/(1+x^10) dx from -pi/2 to pi/2.

Homework Equations


None.

The Attempt at a Solution


sin^7 x means sinx to the 7th power. But how do I find this strange integral? I don't think u-substitution, trig identity, any of them will work.
 
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  • #2
Math9999 said:

Homework Statement


Find the integral of sin^7 x/(1+x^10) dx from -pi/2 to pi/2.

Homework Equations


None.

The Attempt at a Solution


sin^7 x means sinx to the 7th power. But how do I find this strange integral? I don't think u-substitution, trig identity, any of them will work.

Think about symmetry. The interval is symmetric around the origin. What about the integrand?
 
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  • #3
I don't know anything about the integrand.
 
  • #4
Math9999 said:
I don't know anything about the integrand.
Do you know what even and odd functions are?
 
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  • #5
I know that the sine functions are odd, right?
 
  • #6
Math9999 said:
I know that the sine functions are odd, right?

Right. ##\sin(-x)=-\sin(x)##. What about the function you are integrating? What might that have to do with the value of the integral?
 
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  • #7
That sin^7 (x) is also odd.
 
  • #8
Math9999 said:
That sin^7 (x) is also odd.

Right. What about ##\frac{1}{1+x^{10}}##?
 
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  • #9
An even function?
 
  • #10
Math9999 said:
An even function?

You're 100% so far. Now what about their product? The function you are integrating?
 
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  • #11
An odd function.
 
  • #12
Math9999 said:
An odd function.
Exactly. And what do you get when you integrate an odd function from -a to a?
 
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  • #13
0?
 
  • #14
Math9999 said:
0?

I'd feel better if you didn't end every statement with a '?'. Have some confidence!
 
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  • #15
Math9999 said:
0?

Yes, but why? Graphically, it is clear. Can you provide a simple proof?
 
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1. How do I find this integral using the power rule?

The power rule states that the integral of x^n is equal to (x^(n+1))/(n+1) + C, where C is a constant. To use the power rule, you must first rewrite the integral in the form of x^n. Then, simply plug in the value of n+1 and add the constant C.

2. What is the substitution method for finding integrals?

The substitution method involves replacing a variable in the integral with a new variable, and then using the chain rule to solve for the new integral. This method is especially useful when the integral contains functions within functions, such as trigonometric functions.

3. Can I use integration by parts to find this integral?

Integration by parts is a method for finding integrals that involves breaking down the integral into two parts and using the product rule to solve for the integral. This method is particularly useful for integrals that contain products of functions.

4. How do I use trigonometric identities to simplify integrals?

Trigonometric identities can be used to rewrite trigonometric functions in terms of other trigonometric functions, which can make it easier to solve integrals. Common identities include sin^2(x) + cos^2(x) = 1 and tan(x) = sin(x)/cos(x).

5. What is the difference between definite and indefinite integrals?

A definite integral has specific upper and lower limits, while an indefinite integral does not. Indefinite integrals result in a function, while definite integrals result in a numerical value. Additionally, definite integrals are used to find the area under a curve, while indefinite integrals are used to find the antiderivative of a function.

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