Definition
Hypotenuse
In a right triangle, the hypotenuse is the longest side and lies across from the 90° angle.
What it means
Find the small square that marks the right angle. The side directly across from that corner is the hypotenuse. The other two sides meet to make the right angle.
Remember it
Right angle here; hypotenuse across.
Example
A right triangle has shorter sides of 5 cm and 12 cm. Since 5² + 12² = 25 + 144 = 169 = 13², the 13 cm side opposite the right angle is the hypotenuse.
Watch for
A triangle without a right angle has no hypotenuse, even though it still has a longest side.
Common mix-up
Do not name a side the hypotenuse just because it looks longest; first confirm that the triangle has a right angle.
Exact meaning
In a right triangle, the hypotenuse is the side opposite the 90° angle. It is the triangle’s longest side and is the side represented by c in the usual equation a² + b² = c².