What are Double Angle Identities? Trigonometry Trigonometric Identities and Equations Double Angle Identities 1 Answer Wataru Nov 6, 2014 Double Angle Identities sin2theta=2sin theta cos theta cos2theta=cos^2theta-sin^2theta=2cos^2theta-1=1-2sin^2theta tan2theta={2tan theta}/{1-tan^2theta} I hope that this was helpful. Answer link Related questions 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? How can tan 4x be simplified or sec 2x? See all questions in Double Angle Identities Impact of this question 12500 views around the world You can reuse this answer Creative Commons License