TeX source:

\begin{aligned} m=& \frac{f(1+h)-1}{(1+h)-1}=\frac{(1+h)^{2}-1}{h}=\frac{\left\{1+2 h+h^{2}\right\}-1}{h} \\&=\frac{2 h+h^{2}}{h}=2+h .\end{aligned}