Question

How do you express the trig ratio in terms of the same trig ratio of a reference angle: cos 220?

Answer 1

`cos(220^o) = -cos(40^o)`

Explanation:

`220^o = 180^o + 40^o`
So the reference angle is `40^o`

`220^o` is in Quadrant III
So the `cos` is negative (of the 3 primary trig functions only `tan` is positive in Q III).