Concept

Identity

Algebra

In mathematics, an identity is an equality relating one mathematical expression A to another mathematical expression B, such that A and B, which might contain some variables, produce the same value for all values of the variables within a certain domain of discourse. The cited article adds that an identity is an equality between functions that are differently defined, that identities are sometimes indicated by the triple bar symbol instead of the equals sign, and that formally an identity is a universally quantified equality. Theorems stated as identities, such as those relating two expressions for the same quantity, are grouped under this concept together with the wider concept of an equation.

Angle Bisector Theorem

Anne's Theorem

Apollonius's Theorem

Barbier's Theorem

Bezout's Theorem

Brahmagupta Theorem

Bretschneider's Formula

British Flag Theorem

Butterfly Theorem

Carnot's Theorem

Casey's Theorem

Ceva's Theorem

De Gua's Theorem

Descartes Circle Theorem

Euler's Polyhedron Formula

Euler's Quadrilateral Theorem

Garfield's Proof of the Pythagorean Theorem

Gauss-Bonnet Theorem

Geometric Mean Theorem

Heron's Formula

Inscribed Angle Theorem

Intercept Theorem

Intersecting Chords Theorem

Intersecting Secants Theorem

Menelaus's Theorem

Pick's Theorem

Pitot Theorem

Ptolemy's Theorem

Pythagorean Theorem

Riemann-Hurwitz Formula

Riemann-Roch Theorem

Routh's Theorem

Stewart's Theorem

Tangent-Secant Theorem

Theorem of the Gnomon

Van Aubel's Theorem

Van Schooten's Theorem

Viviani's Theorem

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