Answer
The statement makes sense.
Work Step by Step
The provided statement makes sense because consider the following sum of angle identities:
$\begin{align}
& \sin \left( x+y \right)=\sin x\cdot \cos y+\cos x\cdot \sin y \\
& \cos \left( x+y \right)=\cos x\cdot \cos y-\sin x\cdot \sin y \\
\end{align}$
If instead of adding $y\text{ to x}$, add $\text{x to x}$ i.e. replace $y\text{ by x}$:
$\begin{align}
& \sin \left( x+x \right)=\sin x\cdot \operatorname{cosx}+\cos x\cdot \operatorname{sinx} \\
& sin2x=2sinx\cdot cosx \\
& \cos \left( x+x \right)=\cos x\cdot \operatorname{cosx}-\sin x\cdot \operatorname{sinx} \\
& \cos 2x={{\cos }^{2}}x-{{\sin }^{2}}x
\end{align}$
These are the double angle identities.
