How do you verify sin^2 theta cos ^2 theta = 1/8 [1-cos(4 theta)]? Trigonometry Trigonometric Identities and Equations Proving Identities 1 Answer Nghi N. May 25, 2015 Use trig identities: 2sin a.cos a = sin 2a and 2sin^2 a = 1 - cos 2a sin^2 a.cos^2 a = (1/4)(sin^2 2a) = (1/8)(2sin^2 2a) = = (1/8)(1 - cos 4a) 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 11565 views around the world You can reuse this answer Creative Commons License