On Restricted Fourier Series Expansion

A periodic function expressed by 6A.1 f t = f t + T , https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315272351/41040b79-9956-496a-ac34-683fa4364729/content/eqn6a_1.jpg"/> where T is the period, may be expressed in Fourier series as 6A.2 f t = a 0 + ∑ n = 1 ∞ a n cos n ω 0 t + ∑ n = 1 ∞ b n sin n ω 0 t . https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315272351/41040b79-9956-496a-ac34-683fa4364729/content/eqn6a_2.jpg"/>