im not sure which identities to use and how to prove it. 3/18/2014 | Meera from Hightstown, NJ | 2 Answers | 0 Votes Mark favorite Subscribe Comment
You need to put complete question; you missed to in lure the variable x's in your question. The most common trig identity is sin^2(x) + cos^2(x) = 1. Try using that. 3/18/2014 | Chen Jang T. Comment
Solve: cos^2(θ) - sin^2(θ) = 2cos(θ) - 1 cos^2(θ) + sin^2(θ) = 1 [Pythagorean Identity] sin^2(θ) = 1 - cos^2(θ) Substitute in equation to solve: cos^2(θ) - (1 - cos^2(θ)) = 2cos(θ) - 1 2cos^2(θ) - 1 = 2cos(θ) - 1 2cos^2(θ) = 2cos(θ) cos^2(θ) – cos(θ) = 0 cos(θ)(cos(θ) – 1) = 0 Use Zero Product Property: cos(θ) = 0 or cos(θ) = 1 θ = pi/2 + 2n pi, n integer θ = 3 pi/2 + 2n pi, n integer θ = 0 + 2n pi, n integer 3/18/2014 | Steve S. Comment