Evaluate the following integrals:

Assume $x e^{x}=t$

$d\left(x e^{x}\right)=d t$

$\left(e^{x}+x e^{x}\right) d x=d t$

$e^{x}(1+x) d x=d t$

Substituting $\mathrm{t}$ and $\mathrm{dt}$

$\Rightarrow \int \frac{\mathrm{dt}}{\cos ^{2} \mathrm{t}}$

$\Rightarrow \int \sec ^{2} \mathrm{t} \mathrm{dt}$

$\Rightarrow \tan t+c$

But $t=x e^{x}+1$

$\Rightarrow \tan \left(x e^{x}\right)+c$