Question

prove that cos cube A cos 3 A + sin cube a sin 3 is equal to cos cube 2 a

Answer 1

is this the question??

Answer 2

Let A=90 thenPut the value of A in your questionSin(90*3)*sin^3 90 + cos(90*3)*cos^3 90=-1*1+0*0 =-1Now RHS COS^3 2A COS^3(2*90)COS^3(180)=(-1)^3 =-1 HENCE Proved