Answer
$$\cos42^\circ=\cos(30^\circ+12^\circ)$$
The statement is true.
Work Step by Step
$$\cos42^\circ=\cos(30^\circ+12^\circ)$$
Consider $\cos(30^\circ+12^\circ)$
As $30^\circ+12^\circ$ are put inside a parathesis, this means the sum must be carried out first.
And since $30^\circ+12^\circ=42^\circ$,
$$\cos(30^\circ+12^\circ)=\cos42^\circ$$
The statement is thus true.
