Mark the correct alternative in the following: The value of cos (36 o – A) cos (36 o + A) + cos (54 o + A) cos (54 o – A) is

Question

Philoid · Accepted Answer

cos(54^o + A) =sin(36^o – A)

cos(54^o - A) =sin(36^o + A)

cos (36^o–A) cos (36^o+A)+ sin(36^o-A)sin(36^o+A)=cos(2A)