Home/Differential Calculus/L'Hôpital's rule/Formula12.1. L'Hôpital's ruleFormulaIn 12.1. L'Hôpital's ruleFormulaCopy LaTeXlimx→∞f(x)g(x)=limx→∞f′(x)g′(x),f(x)g(x)→0/0 or ∞/∞, f,g differentiable in a neighborhood of ∞, g′(x)≠0 on that neighborhood, limx→∞f′(x)g′(x) exists (finite or ±∞)\lim_{x\to\infty}\frac{f(x)}{g(x)}=\lim_{x\to\infty}\frac{f'(x)}{g'(x)},\qquad \frac{f(x)}{g(x)}\to 0/0\text{ or }\infty/\infty,\ f,g\text{ differentiable in a neighborhood of }\infty,\ g'(x)\neq 0\text{ on that neighborhood},\ \lim_{x\to\infty}\frac{f'(x)}{g'(x)}\ \text{exists (finite or }\pm\infty\text{)}x→∞limg(x)f(x)=x→∞limg′(x)f′(x),g(x)f(x)→0/0 or ∞/∞, f,g differentiable in a neighborhood of ∞, g′(x)=0 on that neighborhood, x→∞limg′(x)f′(x) exists (finite or ±∞)TagsDifferential calculusDerivativeL'Hôpital's ruleLimitDetailSame rule as DIF-114 at infinity; requires form 0/00/00/0 or ∞/∞\infty/\infty∞/∞.VariablesxxxIndependent variablefffFunctiongggSecond function or inner compositionf′f'f′Derivative of fffConditionsf(x)g(x)→0/0 or ∞/∞, f,g differentiable in a neighborhood of ∞, g′(x)≠0 on that neighborhood, limx→∞f′(x)g′(x) exists (finite or ±∞)\frac{f(x)}{g(x)}\to 0/0\text{ or }\infty/\infty,\ f,g\text{ differentiable in a neighborhood of }\infty,\ g'(x)\neq 0\text{ on that neighborhood},\ \lim_{x\to\infty}\frac{f'(x)}{g'(x)}\ \text{exists (finite or }\pm\infty\text{)}g(x)f(x)→0/0 or ∞/∞, f,g differentiable in a neighborhood of ∞, g′(x)=0 on that neighborhood, limx→∞g′(x)f′(x) exists (finite or ±∞)Related topicsIndeterminate limits and L'HôpitalFound an error? Contact us.Related formulasRelatedFormulalimx→af(x)g(x)=limx→af′(x)g′(x),f(x)g(x)→0/0 or ∞/∞, f,g differentiable in a punctured neighborhood of a, g′(x)≠0 on that neighborhood, limx→af′(x)g′(x) exists (finite or ±∞)\lim_{x\to a}\frac{f(x)}{g(x)}=\lim_{x\to a}\frac{f'(x)}{g'(x)},\qquad \frac{f(x)}{g(x)}\to 0/0\text{ or }\infty/\infty,\ f,g\text{ differentiable in a punctured neighborhood of }a,\ g'(x)\neq 0\text{ on that neighborhood},\ \lim_{x\to a}\frac{f'(x)}{g'(x)}\ \text{exists (finite or }\pm\infty\text{)}x→alimg(x)f(x)=x→alimg′(x)f′(x),g(x)f(x)→0/0 or ∞/∞, f,g differentiable in a punctured neighborhood of a, g′(x)=0 on that neighborhood, x→alimg′(x)f′(x) exists (finite or ±∞)Open formulaOpen in sectionRelatedFormula0⋅∞:f⋅g=f1/g or g1/f0\cdot\infty:\quad f\cdot g=\frac{f}{1/g}\ \text{or}\ \frac{g}{1/f}0⋅∞:f⋅g=1/gf or 1/fgOpen formulaOpen in section