How to integrate this formula with secant, exponential, and tangent?

Question

How to integrate this?

$$\int \sec^2(3x)\ e^{\large\tan (3x)}\ dx$$

Answer 1

$$(\tan 3x)'=3\sec^23x\implies\int\sec^23x\,e^{\tan3x}dx=$$

$$=\frac13\int (\tan3x)'e^{\tan3x}dx=\frac13e^{\tan3x}+C.$$

Answer 2

Let $u=\tan 3x$ and $du=3\sec^23x\ dx$, then $$ \int\sec^23x\ e^{\large\tan 3x}\ dx=\frac13\int e^u\ du. $$