Video narration
How do you cross a rectangular field fastest: walk along two sides, or cut diagonally across the corner? That shortcut makes a right triangle: the two sides meeting at the corner form the right angle, and the diagonal is opposite it. That longest side is the hypotenuse. Here’s the rule: the diagonal’s square equals the other two squares added together—a²+b²=c². For sides 3 and 4: 3²+4² equals 9+16, or 25, so c is 5. Your shortcut is five.