Integral of $$$e^{u}$$$

The integral of the exponential function is $$$\int{e^{u} d u} = e^{u}$$$:

$${\color{red}{\int{e^{u} d u}}} = {\color{red}{e^{u}}}$$

Therefore,

$$\int{e^{u} d u} = e^{u}$$

Add the constant of integration:

$$\int{e^{u} d u} = e^{u}+C$$

$$$\int e^{u}\, du = e^{u} + C$$$A