Alphabeta Math

Darboux, L'Hôpital, and Taylor's Theorem

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1 · Prerequisites
2 · Logical flowchart

3 · Items

Definition

Higher derivatives and the classes Cᵏ and C^∞

Theorem

The general Leibniz rule for the n-th derivative of a product

Lemma

Higher-order Rolle theorem

Theorem

Darboux's theorem: every derivative has the intermediate-value property

Corollary

A derivative has neither a removable discontinuity nor a jump discontinuity

Lemma

An injective Darboux function on an interval is strictly monotone

Corollary

An injective or monotone derivative on an interval is continuous

Lemma

Cauchy's mean-value theorem in quotient form when the denominator derivative is nonzero

Theorem

L'Hôpital's rule for the 0/0 form at finite or infinite, one-sided endpoints

Theorem

L'Hôpital's rule for the ∞/∞ form at finite or infinite, one-sided endpoints

Definition

Taylor polynomials and their remainders

Lemma

Taylor polynomials match the prescribed derivatives at the centre

Theorem

Taylor's Schlömilch–Roche remainder formula

Corollary

The Lagrange and Cauchy forms of Taylor's remainder

Theorem

Peano's form: the normalized Taylor remainder tends to zero

Corollary

A uniform derivative bound gives a uniform Taylor remainder bound

Theorem

The second-derivative test for strict local extrema

Theorem

The first nonzero higher derivative classifies a stationary point

Remark

Scope, endpoint, factorial, and deferred-remainder conventions

False statement

If f'(a)=f''(a)=0, then the second derivative test still decides whether a is an extremum

Sources