The above display makes use of an important factor about the exponential function, namely that, as \delta x \to 0 so \displaystyle \frac{e^{\delta x} - 1}{\delta x} \to 1 .

This page uses jsMath
You can get a better display of the maths by downloading special TeX fonts from jsMath. In the meantime, we will do the best we can with the fonts you have, but it may not be pretty and some equations may not be rendered correctly.