Finding trig identity on calculator?

EDIT: I actually went back and re watched the video a few times and realized that he disengaged the bottom two functions. I'm sorry if this took up anyone's time. Can anyone tell me how to graph functions simultaneously on a graphing calculator?

Hi. I'm following along on a precalculus video from my professor. In the very first problem, he graphs a trigonometric equation in the calculator to see if it is an identity. I'm not getting the same graph as he is, and I'm not sure what's wrong. I have it on zoom trig but my graph is different than his.

This is the problem:

Is cos2x = 2(cosx^2)-1 an identity?

Here is the video. It's the very first problem he covers.

142 Section 7.5 Solving Trigonometric Equations - YouTube

Thanks in advance. Please let me know if you need more information.

Re: Finding trig identity on calculator?

is an identity.

Here's a nice proof of the angle sum identity for cosine:

And in the case where then that gives

Q.E.D.