$\quad$ Refer to the graph of $f(x)=2^{x}$ in Figure 18 .
(a) Explain graphically why, for $h>0$, $$ \frac{f(-h)-f(0)}{-h} \leq f^{\prime}(0) \leq \frac{f(h)-f(0)}{h} $$
(b) Use (a) to show that $0.69314 \leq f^{\prime}(0) \leq 0.69315$.
(c) Similarly, compute $f^{\prime}(x)$ to four decimal places for $x=1,2,3,4$.
(d) Now compute the ratios $f^{\prime}(x) / f^{\prime}(0)$ for $x=1,2,3,4$. Can you guess an approximate formula for $f^{\prime}(x) ?$