Question

how do cos n(pi)=(-1^n) ? *fourrier series

Answer 1

well wen n is odd, cos n(pi) is -1
and wen n is even, cos n(pi) is 1

so if you have (-1)^n
you get the same result, wen n is odd u get -1 nd wen n is even you get 1

do you have to use fourier series to prove it?

Answer 2

nope. i asked my friend. (-1)^n is for all values of n. thanks btw

Answer 3

as cos function is +ve in 1st and 4th quadrants only,the value of cos fn is always +ve if n is even and _ve when n is odd.....