The hypotenuse is the longest side of a right triangle, always the side opposite the right angle. Its length relates to the other two sides through the Pythagorean theorem, which is why identifying it correctly is the first step in almost every right triangle problem.
Math Dictionary / Hypotenuse
Hypotenuse
The hypotenuse is the longest side of a right triangle.
GeometryGrade 8Algebra 1GEDSATACT
What it means
It is always across from the right angle.
Also called: longest side of a right triangle
Examples
| In a 3-4-5 right triangle, 5 is the hypotenuse |
| The hypotenuse is labeled c in a^2 + b^2 = c^2 |
| It is across from the 90-degree angle |
Common mistake
The hypotenuse exists only in a right triangle.
Try one
Question: A right triangle has side lengths 5, 12, and 13. Which side is the hypotenuse?
Show answer
13, because it is the longest side.