How do you work out cos omega = 4/5

Question

How do you solve  trig equations that read,

question 1:  cos omega = (4/5)

and,

question 2:  sin omega = 1/3

Answer 1

cos(omega) = 4/5
omega = 2pi*n - cos^-1 (4/5) or = 2pi*n + cos^-1 (4/5), where n is any integer.

sin(omega) = 1/3
omega = 2pi*n + pi - sin^-1 (1/3) or = 2pi*n + sin^-1 (1/3), where n is any integer.