Thread: reduction formula

i have shown

if


then




the next part is hence,find



Im missing something here. I split as etc
but all this does is evaluate the integral in terms of a reduction formula, not using part (a)
What is the trick i am missing to use part (a) and not just evaluate the second integral?

A few questions on and i have to prove a reduction formulae for sin (nx)/sin x

which will kill my problem. But i am still at loss of how to do it with the formula i have derived in part(a)