How do I show that cos4x=18cos(4x)+12cos(2x)+38 I know how to prove that cos2x=12+12cos(2x) by substituting...
How do I show that
I know how to prove that
by substituting with according to the double angle identity
However, how do I do that for ?
Do I do it by writing as
and thus get it by squaring the LHS of
Im not sure how to proceed.