Identifying cos^2 (wt+θ) in Signals Example Problem

[Peon666]

While seeing a signals example problem, I encountered this:

cos^2 (wt+θ) = [1+cos(2wt+2θ)]

What identity is this?

 

[Doc Al]

That doesn't seem right. Looks like they missed a factor of 2:

cos(2x) = 2cos^2(x) - 1