How to solve $$ \int_a^b e^{-\frac{1}{H}(\sqrt{x^2+z^2}-R)}dx$$
z, R, H are constants, a and b are known.
I tried the substitution
$$\displaystyle u=-\frac{\sqrt{x^2+z^2}-R}{H}$$
$$\displaystyle du=-\frac{x}{H\sqrt{x^2+z^2}}dx$$
$$\displaystyle\frac{1}{u'}du=dx$$
and get
$$\displaystyle \int \frac{1}{u'}e^{u}du$$
Then how should I proceed ?