triangle: Quick Facts

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Last updated

Nov. 12, 2026

News •

Consumer complaint leads to paused sales at Triangle gas stations. How to report • Nov. 7, 2026, 9:26 AM ET (The Raleigh News & Observer)

NC swamped by Hurricane Matthew, feds make big booze bust -- Today in NC History • Oct. 15, 2026, 5:00 AM ET (The Raleigh News & Observer)

Photos

A labeled triangle with vertices A, B, and C, sides a, b, and c, and a red line segment h drawn from vertex C perpendicular to side c, representing the height.

Diagram of a right triangle with a yellow interior, green outline, green angle θ, red right-angle square, and sides labeled a, b, and c.

Area of a triangle

Pythagorean theorem

Three theorems of congruent triangles

Figure 6: Construction for similar triangles (see text).

Contrasting triangles in Euclidean, elliptic, and hyperbolic spaces.

Fundamental theorem of similarity

Chinese and Greek geometric theorems

A triangle is inscribed in a circle, with vertices labeled A, B, and C. The central angle theta is shown at the circle's center, formed by two radii meeting at points A and B, illustrating the relationship between the angle and the chord AB.

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Topics

right triangle spherical triangle Pascal’s triangle Heron’s formula trigonometry angle Menelaus’ theorem side-angle-side theorem triangle inequality Ceva’s theorem hexagon

Key People

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Heron of Alexandria

Greek mathematician