henryc0985

hkale pure maths 2006 q8 c(ii)why the summation of the bunch of expression equals to pi(an)/2
i don't understand why in a(i) i calculate the definite integral of cosmxcosnxdx = 0
but there is a non-zero value for the summation of c(ii)

Simon

please post the question here

henryc0985

here is the question and marking

Simon

From part a, what answers do you get?

henryc0985

marking's answer:
a(i) 0
(ii)0 for the first one and pi/2 for the latter one

Simon

for the summation, when m =/= n
then the integral becomes 0
for m = n, the integral becomes pi/2, having a constant of a_n

henryc0985

so that is only the m=n term is left and other terms are equal 0?

Simon

yes, absolutely

henryc0985

thank you very much