Given sintheta=4/5, theta lies in Quadrant II, find cos (theta/2)

Question

This is for my trig class. Thanks for the help!

Answer 1

sin x = 4/5

cos x = -3/5, by 3-4-5 Pythagorean triple and Q. II

cos x/2 = sqrt[(1/2)(1+cos x)] = sqrt[(1/2)(1-3/5)] = sqrt(5)/5