I Do not know how to solve this question?

Question

cos x=-1

we have to solve for x

Answer 1

Hey Abbi!

For this problem it helps to think of the unit circle (I'd recommend getting an image of one to follow along with). On the unit circle, the x-coordinates are cosine values. So to solve cos x = -1, you can simply find the point on the unit circle where x = -1 and then find the angle that that point forms. In this case the only point where x = -1 is the point (-1, 0). To determine the angle we always measure counter clockwise around the unit circle starting from the point (1,0). In this case clockwise and counter-clockwise are both 180° from the point (1,0) so the answer is 180º or π radians. Hope this helps you to think about this type of problem in the future.

-Nathan

Answer 2

Visualize this with the Unit Circle. Cosine is 1 at x=0, Cos(0) = 1

Cosine is -1 at x= π, Cos(π) = -1