Mathematics Atlas

How Proof Is Made
Theorems

Intermediate Value Theorem

Also Known As IVT
Analysis

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Curve Crossing a Line Between Two Points

The intermediate value theorem states that if a continuous function's domain contains an interval [a, b] and s is a number strictly between f(a) and f(b), then there exists some point x between a and b where f(x) equals s. Bernard Bolzano gave the first rigorous proof in 1817.

Facts
Statement
A continuous function defined on a closed interval that takes two different values at its endpoints must take every value between those two endpoint values somewhere inside the interval. 1
Proof Year
1817 1
Cross-Tradition Connections

In Branch

Proved By

Cauchy gave the modern formulation independently, a few years after Bolzano's original proof.

Sources
1. Intermediate Value Theorem (Wikipedia)
Wikimedia Foundationintroductory paragraph
Quote, introductory paragraph
if f is a continuous function whose domain contains the interval [a, b] and s is a number such that f(a)<s<f(b), then there exists some x between a and b such that f(x)=s
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1. Intermediate Value Theorem (Wikipedia)
Wikimedia FoundationHistory section
Quote, History section
The theorem was first proved by Bernard Bolzano in 1817.
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