📐 What Is the Pythagorean Theorem?
8th Grade ➗ Math
In a right triangle, the two short sides squared add up to the long side squared: a² + b² = c².
Right triangles only
The theorem works for right triangles — triangles with one square (90°) corner. The two sides that make the square corner are called legs. The longest side, across from the square corner, is the hypotenuse.
The formula
a² + b² = c². Square each leg, add them, and you get the square of the hypotenuse. For legs 3 and 4: 9 + 16 = 25, and the square root of 25 is 5. So the hypotenuse is 5.
Who was Pythagoras?
Pythagoras was a Greek thinker who lived about 2,500 years ago. People in Babylon, Egypt, India and China also knew this rule — Pythagoras just got his name on it.
Why it is useful
Builders use it to make perfectly square corners, and you can use it to find the shortest distance across a field or a TV screen size.
Quick quiz
In a right triangle, what is the longest side called?
The legs are 6 and 8. How long is the hypotenuse?
Which formula is the Pythagorean theorem?