You can use L'Hôpital’s rule to find a limit when other methods don’t work. In fact, even if some other method does work, L'Hôpital’s rule is often a good shortcut. If substitution of the limit number into the limit expression produces one of the unacceptable forms, ±∞ · 0 or ∞ – ∞, you first have to tweak the problem to get one of the acceptable forms: