Use the information given about the angle theta 0 lessthanor

Use the information given about the angle theta, 0 lessthanorequalto theta lessthanorequalto 2 pi, to find the exact value of the indicated trigonometric function. cos theta = -6/5, tan theta > 0 Find cos (2 theta). A) 5 Squareroot 11/18 B) 7/18 C) -7/18 D)-5 Squareroot 11/18

Solution

csc = -6/5 , tan > 0

sin = 1/csc = -5/6

cos = -11/6

Then cos(2) = 2cos²(x) – 1 = 2*11/36 - 1 = 22/36 - 1 = -14/36 = -7/18