<p>I think I might have used it in the Barron’s Math II book as well (see the diagnostic test). But I’m sure about PR. </p>
<p>Are you saying that you never simplify a function before plugging in the number? </p>
<p>L’Hopital’s rule allows one to eschew simplifying a function (often through factoring and cancelling common factors), which saves a lot of time.</p>