Chapter 4 - Section 4.5 - Graphs of Sine and Cosine Functions - Exercise Set - Page 596: 63

$$y=-2 \sin 2x$$

Looking at the graph, we find that this is the reflected graph of a sine function about the $x$-axis with amplitude $2$ and period $\pi$. So, we conclude that $$A=2, \quad B=\frac{2\pi }{\pi }=2 \\ \Rightarrow \quad y=-A \sin Bx = -2 \sin 2x.$$