Given that tan(x) = -2 and pi/2 < x < pi, find cos 2x.
a. - 4/3
b. - 4/5
c. 3/4
d. - 3/5
tan (x) = - 2
We are in the second quadramt.....so this implies that (x,y) = ( -1, 2)
cos 2x = 1 - 2sin^2 x
sin (x ) = 2 / sqrt [(-1)^2 + 2^2 ] = 2/sqrt (5)
So....sin^2 (x) = 4/5
Then cos 2x = 1 - 2(4/5) = 1 -8/5 = -3/5
+67 
