L’Hôpital’s rule for indeterminate limits

E928482

L’Hôpital’s rule for indeterminate limits is a fundamental calculus technique that evaluates certain indeterminate forms of limits by relating them to the limits of the derivatives of the functions involved.

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L’Hôpital’s rule 1

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Predicate Object
instanceOf calculus rule
limit evaluation technique
mathematical theorem
alternativeName L’Hospital’s rule NERFINISHED
alternativeSpelling L’Hospital’s rule for indeterminate limits NERFINISHED
appliesTo indeterminate form 0/0
indeterminate form ∞/∞
assumes real-valued functions in a neighborhood of the point
canBeAppliedRepeatedly true
category techniques for evaluating limits
doesNotApplyTo determinate limits
field calculus
mathematical analysis
generalizationOf Cauchy’s mean value theorem NERFINISHED
hasVariant version for limits at infinity
version for one-sided limits
version for sequences via continuous extension
historicalAttribution first published in 1696 in l’Hôpital’s textbook "Analyse des Infiniment Petits"
indirectlyUsedFor indeterminate form 0^0 via logarithms
indeterminate form 0·∞ via algebraic manipulation
indeterminate form 1^∞ via logarithms
indeterminate form ∞^0 via logarithms
indeterminate form ∞−∞ via algebraic manipulation
isGeneralizedBy Cauchy’s mean value theorem proof
isOftenMisusedBy applying when hypotheses fail
isTaughtIn AP Calculus curriculum
introductory calculus courses
university analysis courses
namedAfter Guillaume de l’Hôpital NERFINISHED
proofUses Cauchy mean value theorem NERFINISHED
mean value theorem NERFINISHED
relatedTo Taylor series methods for limits
asymptotic analysis
relates limit of a quotient to limit of derivative quotient
requires denominator derivative nonzero on a punctured neighborhood
existence of limit of derivative quotient or divergence to ±∞
functions differentiable on an open interval around the point
requiresCondition derivative quotient limit must exist or be infinite
original limit must be in an indeterminate form
statement If lim_{x→a} f(x)=0 and lim_{x→a} g(x)=0 and f,g are differentiable near a with g′(x)≠0, then lim_{x→a} f(x)/g(x)=lim_{x→a} f′(x)/g′(x) when the latter limit exists or is infinite.
If lim_{x→a} |f(x)|=∞ and lim_{x→a} |g(x)|=∞ and f,g are differentiable near a with g′(x)≠0, then lim_{x→a} f(x)/g(x)=lim_{x→a} f′(x)/g′(x) when the latter limit exists or is infinite.
typicalExample lim_{x→0} (sin x)/x = 1 via derivatives cos x / 1
lim_{x→∞} (ln x)/x = 0 via derivatives 1/x / 1
usedFor evaluating difficult limits
resolving 0/0 indeterminate forms
resolving ∞/∞ indeterminate forms
usesConcept derivative
differentiability
limit

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Full triples — surface form annotated when it differs from this entity's canonical label.

Guillaume de l’Hôpital notableConcept L’Hôpital’s rule for indeterminate limits
Guillaume de l’Hôpital ruleNamedAfter L’Hôpital’s rule for indeterminate limits
this entity surface form: L’Hôpital’s rule