Question

cos^-1 sqrt 2/2

Answer 1

ask yourself the following question:
do you know an angle (number) whose cosine is \(\frac{\sqrt{2}}{2}\) ?

Answer 2

or look at the last page of the attached cheat sheet. find the point on the upper half of the unit circle where the first coordinate is \(\frac{\sqrt{2}}{2}\)and then look to see what the angle is