Graph the function $y=2 \cos 2 x$ for $-2 \leq x \leq 3.5 .$ Then, on the same screen, graph
$$y=\frac{\sin 2(x+h)-\sin 2 x}{h}$$
for $h=1.0,0.5,$ and $0.2 .$ Experiment with other values of $h$ including negative values. What do you see happening as $h \rightarrow 0 ?$ Explain this behavior.