Question

How do you find the two quadrants that `theta` could terminate given `costheta=1/2`?

Answer 1

Quadrants `1` and `4`.

Explanation:

Since `costheta=1/2`, we know `theta=1/3pi` or some complement of the angle. `1/3pi` is in the first quadrant and the equivalent angle which would give `costheta=1/2` is `2pi-1/3pi=5/3pi` which is in the fourth quadrant.

As already stated, any complementary angles to these two would have to be in either quadrants `1` or `4`.