How do you verify cos^2 2A = (1+cos4A)/2cos22A=1+cos4A2? Trigonometry Trigonometric Identities and Equations Proving Identities 1 Answer Bdub May 11, 2016 see below Explanation: Use Property: cos2A=2cos^2A-1cos2A=2cos2A−1 Right Hand Side :=(1+cos4A)/2=1+cos4A2 =(1+cos2(2A))/2=1+cos2(2A)2 =(1+(2cos^2(2A)-1))/2=1+(2cos2(2A)−1)2 =(1-1+2cos^2(2A))/2=1−1+2cos2(2A)2 =(cancel1-cancel1+2cos^2(2A))/2 =(2cos^2(2A))/2 =(cancel2cos^2(2A))/cancel2 =cos^2(2A) = Left Hand Side Answer link Related questions What does it mean to prove a trigonometric identity? How do you prove \csc \theta \times \tan \theta = \sec \theta? How do you prove (1-\cos^2 x)(1+\cot^2 x) = 1? How do you show that 2 \sin x \cos x = \sin 2x? is true for (5pi)/6? How do you prove that sec xcot x = csc x? How do you prove that cos 2x(1 + tan 2x) = 1? How do you prove that (2sinx)/[secx(cos4x-sin4x)]=tan2x? How do you verify the identity: -cotx =(sin3x+sinx)/(cos3x-cosx)? How do you prove that (tanx+cosx)/(1+sinx)=secx? How do you prove the identity (sinx - cosx)/(sinx + cosx) = (2sin^2x-1)/(1+2sinxcosx)? See all questions in Proving Identities Impact of this question 8327 views around the world You can reuse this answer Creative Commons License