Question

What is the principal value cost of cos​−1 ​(0.69)

Answer 1

We are asked to find the principal value of
cos ⁻¹ (0.69)
which is just the least positive angle
cos ⁻¹ (0.69) = 46.37°
Other values of 
cos ⁻¹ (0.69) is
46.37° - 180° n
where n is a whole number