Question
Evaluate: $\int \frac{e^x(1+x)}{\cos ^2\left(x e^x\right)} d x$

Answer

Let $I =\int \frac{e^x(1+x)}{\cos ^2\left(x e^x\right)} d x$
Put $x.e^x = t$
Diff.$w.r.t..x$
$ \therefore x \cdot e^x+e^x \cdot 1=\frac{d t}{d x}$
$ \therefore e^x(1+x) d x=d t$
$ \therefore I=\int \frac{d t}{\cos ^2 t}=\int \sec ^2 t d t$
$ \therefore \tan t+c$
$ =\tan \left( x \cdot e ^{ x }\right)+ e $

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