Please answer the question in the image and please show all your steps.

Problem 4. The complex Fourier series for a function defined on [-L, L] is, f (20) = E Cne-innx/ L n=-00 with coefficients L Cn = f(x)einux/L dx . 2L -L The on are related to the non-complex Fourier coefficients with on = ?(an + ibn). If f (x) is real and even, prove that coefficients on and c_n are real and that Cn = C_n