a_0=\frac{1}{T}\int_{-\frac{T}{2}}^{\frac{T}{2}}s(t) dt

a_n=\frac{2}{T}\int_{-\frac{T}{2}}^{\frac{T}{2}} s(t) cos(n \omega_0 t) dt

b_n=\frac{2}{T}\int_{-\frac{T}{2}}^{\frac{T}{2}} s(t) sin(n \omega_0 t) dt