Exponential integral question How would I solve the following problem?
$$f(x)=\int\!\frac{4}{\sqrt{e^x}}\,dx$$
Using $u$ substitution I have set $u=e^x$ andd $du=e^x dx$
so would I have $$4\int\!\frac{du}{\sqrt{u}}$$
What would I do from here?

Notice: You may use your method, but in doing so, recall that $\color{blue}{u=e^x}$ andd $du=e^x dx \implies  dx = \dfrac{du}{\color{blue}{\bf e^x}} = \dfrac{du}{\color{blue}{\bf u}}$
This gives us
$$4\int \frac{1}{\sqrt{u}}\frac{du}{u}=4\int u^{-3/2}\,du$$
