How do you simplify #1-2sin^2 ( theta / 3 )# using the double angle identities? Trigonometry Trigonometric Identities and Equations Double Angle Identities 1 Answer Nghi N. Jan 18, 2016 #cos ((2x)/3)# Explanation: Use identity: #cos 2a = 1 - 2sin^2 a# #1 - 2sin^2 (x/3) = cos ((2x)/3)# Answer link Related questions What are Double Angle Identities? How do you use a double angle identity to find the exact value of each expression? How do you use a double-angle identity to find the exact value of sin 120°? How do you use double angle identities to solve equations? How do you find all solutions for #sin 2x = cos x# for the interval #[0,2pi]#? How do you find all solutions for #4sinthetacostheta=sqrt(3)# for the interval #[0,2pi]#? How do you simplify #cosx(2sinx + cosx)-sin^2x#? If #tan x = 0.3#, then how do you find tan 2x? If #sin x= 5/3#, what is the sin 2x equal to? How do you prove #cos2A = 2cos^2 A - 1#? See all questions in Double Angle Identities Impact of this question 4190 views around the world You can reuse this answer Creative Commons License