How to solve

f$($x$)=\{$x$,0\backslash$pi $\}$

$\{,\backslash$pi $\}$ and has period $2$

a$)$ Obtain Fourier Series coefficients of periodic function f$($x$).$

b$)$ Plot the approximated function by using first $5,20$ and $50$ coefficients. Show the error function.