How do you integrate int xsin2xxsin2x by parts from [0,pi][0,π]?

1 Answer
Feb 5, 2017

int_0^pi xsin2x dx =-pi/2π0xsin2xdx=π2

Explanation:

Consider the integral:

int_0^pi xsin2x dxπ0xsin2xdx

Note that:

d(-1/2cos2x) = sin2x dxd(12cos2x)=sin2xdx

so we can integrate by parts:

int_0^pi xsin2x dx = int_0^pi xd(-1/2cos2x)π0xsin2xdx=π0xd(12cos2x)

int_0^pi xsin2x dx = [-(xcos2x)/2]_0^pi +1/2 int _0^pi cos2x dxπ0xsin2xdx=[xcos2x2]π0+12π0cos2xdx

int_0^pi xsin2x dx = [-(xcos2x)/2]_0^pi +1/4 [sin2x]_0^pi π0xsin2xdx=[xcos2x2]π0+14[sin2x]π0

int_0^pi xsin2x dx = [-(picos(2pi))/2 +0] + [0 -0]π0xsin2xdx=[πcos(2π)2+0]+[00]

int_0^pi xsin2x dx =-pi/2π0xsin2xdx=π2