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

Question

can you find the answer to 4 decimals? any help is awesome :)

Answer 1

So Matthew B.,

cos(x) = 11/15; use identity for cos (2.theta.) = cos^2(x)-sin^2(x) to extend that. If you don't know such identities right off the bat, you SHOULD know that they exist, and look them up.

-- Cheers, --Mr. d.