Find the exact value of cos2theta if sin2theta=3/4 and theta is between 0 and 90 degree

When you are making a circle graph by hand, how do you convert a number for a part into its corresponding angle measure in the circle graph? when you are making a circle graph by hand, what should you do if one of your angle measures is greater than 180°?

Simplify (1/2)4th power a. (1/16) b.(1/8) c.(1/4)

Can someone answer this question for me