Definition: The hypotenuse is the longest side of a right triangle, located directly opposite the right angle.
What is the hypotenuse?
In a right triangle, two sides form the 90 degree corner, the legs, and the third side across from the corner is the hypotenuse.
How do you identify it?
Find the right angle, then look across. It is always the longest side. If a triangle has sides 6, 8, and 10, the hypotenuse is 10 and the legs are 6 and 8.
How do you compute it?
Use c = the square root of (a2 + b2). For legs 20 and 21, c is the square root of 400 + 441 = 841, which is 29.
Why can it not be a leg?
In a right triangle, c2 = a2 + b2, so c2 is greater than each of a2 and b2. That makes c the largest.
Where is it useful?
Mathbot checks the diagonal of a rectangular screen 16 inches wide and 12 inches tall. The diagonal is the hypotenuse: the square root of 256 + 144 = 400, so 20 inches.
What is a common mistake?
Assuming the longest side is the hypotenuse in any triangle. The word is used only in right triangles.