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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Homework Help Overview

The discussion revolves around evaluating the integral of sin^7 x/(1+x^10) from -π/2 to π/2. Participants are exploring the properties of the integrand and its behavior over the symmetric interval.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the nature of the integrand, questioning its symmetry and the implications of the sine function's properties. There is a focus on identifying whether the integrand is odd or even and how that affects the integral's value.

Discussion Status

The discussion has progressed towards understanding the characteristics of the integrand, with several participants affirming that sin^7 x is an odd function. The implications of this property on the integral's value are being explored, with some participants suggesting that the product of the functions involved leads to an odd function overall.

Contextual Notes

Participants are considering the symmetry of the integral's limits and the properties of odd and even functions as part of their reasoning process. There is a recognition of the need for a clear explanation of why integrating an odd function over a symmetric interval results in zero.

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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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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I don't know anything about the integrand.
 
Math9999 said:
I don't know anything about the integrand.
Do you know what even and odd functions are?
 
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I know that the sine functions are odd, right?
 
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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That sin^7 (x) is also odd.
 
Math9999 said:
That sin^7 (x) is also odd.

Right. What about ##\frac{1}{1+x^{10}}##?
 
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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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