the information given about the angle theta theta lessthanor

the information given about the angle theta, theta lessthanorequalto theta lessthanorequalto 2 pi, to find the exact value ot the indicated trigonometric cos theta = - 3/5, sin theta > 0 Find cos theta/2

Solution

15. cos theta=-3/5       and sin theta is positive.

In second quadrant cosine is negative and sine is negative

cos(theta/2)= sqrt((1+cos theta)/2)

                   = sqrt((1-3/5)/2) = sqrt(2/10)