The hypotenuse is the longest side in a right triangle. Let's break it down to understand why!

1. What is the hypotenuse?
   The hypotenuse is the side across from the right angle.

2. About Angles:
   In a right triangle, the biggest angle is always 90 degrees.

3. Triangle Rule:
   The lengths of the two shorter sides (called legs) must add up to more than the length of the hypotenuse.

So, because the hypotenuse is across from the biggest angle, it has to be longer!

For example, if the two legs have lengths of $a$ and $b$, the hypotenuse $c$ follows this rule:

$c^2 = a^2 + b^2$

This means that $c$ will always be longer than either $a$ or $b$.