sin(2x) = 2 sin(x) cos(x) = 2 ( -8/17)(15/16) = -240/289
cos(2x) = 1 - 2* sin^2(x) = 1 - 2 (-8/17)^2 = 1 - 2(64/289) = 1 - 128/289 = 161/289
tan(2x) = 2 tanx / (1-tan^2(x)) = 2 * (-8/15) / ( 1 - (-8/15)^2)
= -16/15 / ( (225 - 64)/225
=16/15 * 225/161 = 240/161