Question

I am still new to trigonometry.. Can I have clear explanation for this question please ?

By considering the graph y= cos x, or otherwise, express the following in terms of cos x .

(a) cos( 360-x)
(b) cos (x+180)

Answer 1

For cos(x+180)
If you draw the graph and look at when x=0, then cos(x+180) = -1. Whereas cos(x) = 1.
So cos(x+180) = - cos(x)

Answer 2

Have you seen the trigonometric circle yet ?

Answer 3

No actually

Answer 4

This is what it looks like:
You'll notice that cos(x) and cos(360-x) have the same value.