Question #fc331 Trigonometry Trigonometric Identities and Equations Proving Identities 1 Answer P dilip_k Dec 20, 2016 Given #sinx+siny=1/4# #=>2sin((x+y)/2)cos((x-y)/2)=1/4......(1)# Also given #cosx+cosy=1/3# #=>2cos((x+y)/2)cos((x-y)/2)=1/3..........(2)# Dividing (1) by (2) we get #tan((x+y)/2)=3/4# Now #cot(x+y)=1/(tan(x+y))# #=(1-tan^2((x+y)/2))/(2tan((x+y)/2))# #=(1-(3/4)^2)/(2xx3/4)# #=((16-9)/16)/(3/2)# #=7/16*2/3=7/24# 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 2607 views around the world You can reuse this answer Creative Commons License