Question

(cos3x)^2+(sin3x)^2=cos(f(x))

find f(x)

Answer 1

\[
(\cos3x)^2+(\sin3x)^2=1
\]

Answer 2

So I guess...\[
1=\cos(f(x)) \\
\arccos(1) = f(x)
\]

Answer 3

It's a very strange problem.