How do you prove #(1-tantheta)/(1+tantheta)=(cottheta-1)/(cottheta+1)#? Trigonometry Trigonometric Identities and Equations Proving Identities 1 Answer Bdub Oct 5, 2016 see below Explanation: #(1-tan theta)/(1+tan theta) = (cot theta -1)/(cot theta +1)# Right Side: #= (cot theta -1)/(cot theta +1)# #=(1/tan theta -1)/(1/tan theta +1)# #=((1-tantheta)/tan theta)/((1+tan theta)/tantheta)# #=(1-tantheta)/tan theta * tan theta/(1+tan theta)# #=(1-tan theta)/(1+tan theta)# #=#Left 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 20181 views around the world You can reuse this answer Creative Commons License