<PRE><B>Question 1202708</B>
.


See this link


https://math.stackexchange.com/questions/2090023/calculate-fourier-series-of-fx-x2-x-in-pi-pi



See also the solution by Diana Ferreira under this link


https://www.quora.com/How-can-I-find-the-Fourier-series-for-the-function-F-x-x%C2%B2-in-the-interval-%CF%80-x-%CF%80-and-deduce-that-%CF%80%C2%B2-8-1-1-3%C2%B2-1-5%C2%B2-1-7%C2%B2-1-9%C2%B2



</PRE>