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Math Help - integral problem

  1. #1
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    integral problem

    Hello, can someone help me on this one, please?

    integral from negative pi to pi of cos mx times cos nx dx
    where m and n are positive integers.

    I guess the answer is pi if m = n and zero otherwise.

    Thanks!

    ZD
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  2. #2
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    Quote Originally Posted by ZeroDivisor View Post
    Hello, can someone help me on this one, please?

    integral from negative pi to pi of cos mx times cos nx dx
    where m and n are positive integers.

    I guess the answer is pi if m = n and zero otherwise.

    Thanks!

    ZD
    Use the equality:  \cos(mx)\cos(nx)=\frac{1}{2}[\cos(m+n)x+\cos(m-n)x]
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  3. #3
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    Thank you curvature!
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  4. #4
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    Quote Originally Posted by curvature View Post
    Use the equality:  \cos(mx)\cos(nx)=\frac{1}{2}[\cos(m+n)x+\cos(m-n)x]
    Did you mean  \cos(mx)\cos(nx)=\frac{1}{2}[\cos((m+n)x)+\cos((m-n)x)] ?
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  5. #5
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    We can use this method to find out the coefficient of cosnx in Fouriee series
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