Question

How do you find all solutions to `cos 3x= -0.78` on [0,2pi)?

Answer 1

`47^@09 and 312^@91`

Explanation:

Calculator and trig unit circle give -->
`cos 3x = -0.78` ---> `3x = +- 141^@26`
a. 3x = 141.26 ---> `x = 47^@09`
b. 3x = - 141.26 --> x = - 47.09, or `312^@91` (co-terminal)