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HashBrowns
Poster

Post Number: 9
Posted on Saturday, 16 June, 2012 - 05:47 pm:   

I am stuck on this problem.

Prove that for values of 2a to 0 for x, Integral (f(x)) dx = Integral for values of a to 0 for x, of (f(x) + f(2a-x)) dx.

Hence, find Integral from pi to 0, of xsin(x)sin(3x) dx

I found xsin(x)sin(3x)= xsin^2(2x) - xsin^2(x), but am confused on how to reach the suggested value of the integral = 0.

I would be grateful for any help.
Simon Taylor
Veteran poster

Post Number: 670
Posted on Monday, 18 June, 2012 - 03:46 pm:   

Before trying any trig identities, how about applying the rule you just found to the integral?

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