Question

How do you evaluate `arccost(-sqrt3 /2)`?

Answer 1

Find `arccost ((-sqrt3)/2)`

Explanation:

Trig table gives ->

`cos t = (-sqrt3/2)` --> arc `t = (5pi)/6` or 150 deg

Trig unit circle gives another arc t that has the same cos value.

`t = - (5pi)/6 or (7pi)/6`

Answer: within period `(0, 2pi)`, there are 2 answers: `(5pi)/6 and (7pi)/6`