Question

Find an identity for cos(4t) in terms of cos(t)?

Answer 1

I don't get it?

Answer 2

\[\frac{ -\sin(8t) }{\cos(8t)-1 }\]

Answer 3

The double angle formula for cos says that\[\cos(2A)=2\cos^2A-1\] so \[\cos(4t)=\cos(2(2t))=2\cos^2(2t)-1\]