Answer
The answer to Exercise 87 is the negative of $y=-sin{2x}$.
Work Step by Step
From Exercise 87, we got $y=\sin{(-2x)} = -\sin{2x}$, which means that $y=\sin{(-2x)}$ is equivalent to $y=-\sin{2x}$
Note that $-\sin{2x}$ is just the opposite (or negative or additive inverse) of $\sin{2x}$.
Therefore, the answer in Exercise 87 is the negative of $y=-\sin{2x}$.
