which is the integral for exp( -a/x ) dx ?
i have tried every method
Topsquark is correct.
It is a famous case that,
We shall convert this integral into this form.
For simplicity sake we shall use , thus,
Manipulate it as,
Let, (going to apply the substitution rule)
If you use integration by parts with,
We have converted this integral into an integral which has no elementary anti-derivative. This confirms topsquarks guess.