How do you verify #cos (x-y) - cos (x+y) = 2 sin x sin y#? Trigonometry Trigonometric Identities and Equations Proving Identities 1 Answer Bdub May 13, 2016 see below Explanation: Use Properties: #cos(A+B)=cosAcosB-sinAsinB# #cos(A-B)=cosAcosB+sinAsinB# Left Side: #=cos(x-y)-cos(x+y)# #=cosxcosy+sinxsiny-(cosxcosy-sinxsiny)# #=cosxcosy+sinxsiny-cosxcosy+sinxsiny# #=2sinxsiny# #=#Right 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 26621 views around the world You can reuse this answer Creative Commons License