Originally Posted by

**StefanM** I want to find the fourier series for the following function:

f(t)= cost (t) t>=0 and = 0 cos(t)<0

This is pretty unclear: did you mean f(t) = cos(t) when t >= 0 , and f(t) = 0 when t < 0, or you did mean f(t) = cos(t) whenever cos(t) >= 0 ,and

f (t) = 0 otherwise? I think it should be the second one since then the function is clearly periodic, but you better make it clearer.

Tonio

Now since the function is 2pi periodic and even the sin coeff will be 0 and I need only to calculate the fourier cosine.

But what should I use for limits?Becuase the coefficient,defined by the integral between the function and cos(kt), will be equal to cos(kt)sin(t),which is 0 if the integral is defined from 0 to pi os 2pi=>the fourier cosine to be equal to 0.Any help?