Question

Show how the double angle formula for cosine is derived from the sum formula?

Answer 1

well:\[\cos(2x)=\cos(x+x)\]

Answer 2

and then the sum formula is used on x+x

Answer 3

actually it should be:\[\cos^2x-\sin^2x\]

Answer 4

\[\cos(x+x)=\cos(x)*\cos(x)-\sin(x)*\sin(x)\]

Answer 5

Ok