<p>So im taking the calc ab exam next week, and i have a question on solving limits. All of my prep books give a gazillion different methods of solving limits, but none really mention l hopitals rule, ahich seems much simpler to me. Is there a reason? </p>
<p>L’Hopital’s rule isn’t specifically covered on the AB Test. There are some problems you can solve using that method, but technically all of them can be solved without L’Hopital’s rule (although I agree that L’Hopital’s rule is simpler, and I used that method on a few problems last year when I took the exam). </p>
<p>Thanks! </p>
<p>Remember you can only use L’Hôpital’s rule to find lim f(x)/g(x) if lim f(x) = lim g(x) = 0 or infinity. You are allowed to use L’Hôpital’s rule; just be careful when you use it, and note that every limits problem on AB can be solved without L’Hôpital’s rule.</p>
<p>I don’t know that rule, but my teacher told me that for some limit problems with x-># can be solved by taking the derivative of both the top and bottom individually of the equation (NOT quotient rule) and then pluging in the value. This is usually specific if the bottom is 0 by just plugging in the x value</p>
<p>As above, you can only use that rule (L’Hôpital’s) if initially, you obtain 0/0 or infinity/infinity, and if lim_{x -> c} f’(x)/g’(x) exists (see Wikipedia article). It may not work on other cases:</p>
<p>Ex. lim_{x -> 0+} (x^2 + 1)/x. If you plug in x = 0, you obtain 1/0, and blindly taking derivatives of numerator and denominator yields an incorrect answer of 0.</p>