Posted by Moe on Saturday, April 27, 2013 at 9:51pm.
quadrant 2
cos 2y = 1 - 2 sin^2 y
but sin y = 3/5 (3 4 5 triangle)
cos 2 y = 1 - 2 (3/5)
= 1 - 6/5
= -1/5
last 3 lines should be
cos (2y) = 1 - 2(3/5)^2
= 1 - 18/25 = 7/25 or .28
Whoops, thank you