Use the even-odd identities to evaluate the expression. cos ⁡ ( − θ ) − cos ⁡ θ \cos\left(-\theta\right)-\cos\theta cos ( − θ ) − cos θ

Here we're asked to use our even odd identities in order to evaluate the expression. And here our expression is the cosine of negative theta minus the cosine of theta. Now using my even odd identity here, I'm gonna replace this negative argument. Now the cosine of negative theta is simply the cosine of theta. So this ends up being the cosine of theta minus the cosine of theta. Now if I subtract that thing from itself I end up with 0 so the cosine of theta minus the cosine of theta is simply 0 and we're done here. The cosine of negative theta minus the cosine of theta is 0. Thanks for watching and I'll see you in the next one.