How do you prove #1- [(cos^(2)x)/(1+sinx)]= sinx#? Trigonometry Trigonometric Identities and Equations Proving Identities 1 Answer Alan P. Apr 15, 2015 By the Pythagorean Theorem #cos^2(x) + sin^2(x) = 1# or #cos^2(x) = 1-sin^2(x)# So #1-[(cos^2(x))/(1+sin(x))]# #= 1- [(1-sin^2(x))/(1+sin(x))]# #=1 - [((1-sin(x))*(1+sin(x)))/(1+sin(x))]# #= 1- [1-sin(x)]# #= sin(x)# 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 28015 views around the world You can reuse this answer Creative Commons License