Question

How do you find the exact value of `cos(theta) = -1`?

Answer 1

We don't really find it so much as just know it's `theta = 180^circ + 360^circ k quad` for integer `k`.

Explanation:

How do we really know `cos 180^circ = -1`? Perhaps the supplementary angle formula:

`cos(180^circ - theta) = - cos theta`

`cos(180^circ - 0^circ) = -cos 0^circ = -1 quad sqrt`