If sec ( x ) = 15 11 (in Quadrant-I), find cos ( 2 x ) =

Answer 1

secx = 15/11

cosx = 11/15

sinx = sqr104/15 = about 10.2/15

cos2x = cos^2(x) - sin^2(x) = (11/15)^2 - 104/225 = 121/225 - 104/225 = 117/225

cos2x = 117/225= 0.52