Let x(t) be a periodic function with period T=10. The Fourier series coefficients for this series are denoted by a_k, that is x(t)=∑_k=-∞^∞a_ke^jk(2π/T)t. The same function x(t) can also be considered as a periodic function with period T'=40. Let b_k be the Fourier series coefficients when period is taken as T'. If ∑_k=-∞^∞|a_k|=16 then ∑_k=-∞^∞|b_k| is equal to