Fourier Series of Triangular waveform

this is the solution of Fourier series of a triangular waveform from the book Circuits and Networks: Analysis and Synthesis by Shyammohan S. Palli. In this problem they have take the time period of the triangular waveform from -π to +π instead of 0 to 2π.
Now, from -π to 0 the equation of the waveform is as shown below
and from 0 to +π the equation of the waveform is
If i take the interval from 0 to 2π.then from 0 to +π the equation of the waveform will be
and from +π to +2π the equation of the waveform will be
But this gives
which did not match with previous.My question is why they took the interval from -π to +π instead of 0 to 2π.
I will post my calculation here




