Representing cos(npi/2) in general form

1. Feb 26, 2012

nutcase21

hi i am currently trying to solve a fourier series question and i realise for example cos(npi) can be represented as (-1)n.

So i was wandering is there anyway to represent cos(npi/2) to a general form too?

2. Feb 26, 2012

Office_Shredder

Staff Emeritus
i suppose something like
(1+(-1)n)/2*(-1)n/2

3. Feb 26, 2012

nutcase21

OIC thnks.

is there any tricks to getting the general form?