Graphing a Fourier Series on a TI-84 Plus not working so well

[QuantumPixel]

Hi!

I was wondering how you would graph a Fourier series for a square wave that periodic. My textbook gave something proper that I would expect (just google 'Square Wave Fourier Series Expansion') while my TI - 84 gave a image like the one somewhere in this thread. It would be nice if anybody could help me fix this.

My TI 84 screen:

QuantumPixel

 

[HallsofIvy]

what interval is the period? How many terms did you take for the series?

 

[QuantumPixel]

what interval is the period? How many terms did you take for the series?

Between the intervals of [-1,1] and 11 terms.