Answer
See step by step proof below.
Work Step by Step
We prove the equation by substituting the function $f(x)=10^x$ to the left side of the expression:
$\frac{f(x+h)-f(x)}{h}=\frac{10^{x+h}-10^x}{h}=\frac{10^x10^h-10^x}{h}=\frac{10^x(10^h-1)}{h}$
Thus we proved that $\frac{f(x+h)-f(x)}{h}=10^x(\frac{10^h-1}{h})$
