Use zooming to investigate $f^{\prime}(0)$, the slope of the curve $y=f(x)$ at $x=0$, for the following two functions.
a.
$$
f(x)= \begin{cases}x \sin \left(\frac{1}{x}\right), & \text { if } x \neq 0 \\ 0, & \text { if } x=0\end{cases}
$$
b.
$$
f(x)= \begin{cases}x^2 \sin \left(\frac{1}{x}\right), & \text { if } x \neq 0 \\ 0, & \text { if } x=0\end{cases}
$$