To solve Fourier Series problems you launch Differential Equations Made Easy go to menu option 4 : Transforms
There, select the last option “Fourier Series”
Now enter the function f(x) and the given interval [a,b]
Notice you can either type in pi or the actual pi symbol, it will both work.
You now see the definition of the Fourier Series using the cos and sin terms.
And finally, you will get the correct Fourier Series of the given function f(x) :