Determine the exact values

Question

Given that Cos x=(4/5) and 0 degrees< x < 90 degrees.

determine the exact values of sin (x/2), cos (x/2) and tan (x/2).

be sure to rationalize your answer and show your work.

Answer 1

If cos x = 4/5 then sin x = 3/5

You can either use the half-angle formulae or actually look up x in trig tables (or calculator), divide the angle in half and look up the trig functions required.