# Thread: L'Hospital's rule not applicable?

1. ## L'Hospital's rule not applicable?

Hi,

I'm doing curve sketching and am trying to find vertical asymptotes for f(x) = 2 - 15x + 9x^2 -x^3

I haven't studied L'H Rule for too long but I see that the lim as x approaches infinity would be 2 - infinity + infinity - infinity and wouldn't that be an indeterminate form? I can see that there are no asymptotes but any clarification on solving this type of limit is appreciated

Looking at it again I'm guessing that the above solution is negative infinity since the function's highest power would go to negative infinity?

2. Originally Posted by DannyMath
Hi,

I'm doing curve sketching and am trying to find vertical asymptotes for f(x) = 2 - 15x + 9x^2 -x^3

I haven't studied L'H Rule for too long but I see that the lim as x approaches infinity would be 2 - infinity + infinity - infinity and wouldn't that be an indeterminate form? I can see that there are no asymptotes but any clarification on solving this type of limit is appreciated

Looking at it again I'm guessing that the above solution is negative infinity since the function's highest power would go to negative infinity?
You are sketching a cubic equation graph. I suggest you review your class notes, textbook, on-line resources etc. There are no asymptotes. l'Hopspital's is completely irrlevant here.