Odd Integration Log Out | Topics | Search
Moderators | Register | Edit Profile

Ask NRICH » Archive 2011-2012 » Onwards and Upwards » Odd Integration « Previous Next »

Author Message

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?

Add Your Message Here
Posting is currently disabled in this topic. Contact your discussion moderator for more information.

Topics | Last Day | Last Week | Tree View | Search | Help/Instructions | Program Credits Administration