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A right triangle has exactly one 90-degree angle. Learn the definition, the names of its sides (legs and hypotenuse), and the Pythagorean theorem that defines its side lengths.
The defining feature of a right triangle is its single right angle. The two sides forming that angle are the legs; the side opposite it — always the longest — is the hypotenuse.
Right triangles are governed by the Pythagorean theorem and host the basic trigonometric ratios (sine, cosine, tangent). Special cases like the 30-60-90 triangle have fixed side ratios.
A right triangle is a triangle with exactly one 90-degree (right) angle. The side opposite that angle is the hypotenuse; the other two sides are the legs.
The Pythagorean theorem: a² + b² = c², where a and b are the legs and c is the hypotenuse. It works only for right triangles.