Mathematics
What is The Pythagorean theorem?
The Pythagorean theorem states that in a right-angled triangle, the square of the longest side (the hypotenuse) equals the sum of the squares of the other two sides: a² + b² = c². It lets you find an unknown side when you know the other two.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains the pythagorean theorem.
Key things to understand
- 1It only applies to right triangles — triangles with one 90° angle.
- 2The hypotenuse (c) is always the side opposite the right angle and is the longest side.
- 3Example: if a = 3 and b = 4, then c = √(9 + 16) = √25 = 5.
- 4It's used everywhere from construction and navigation to computer graphics and measuring distances.
Frequently asked questions
- Who was Pythagoras?
- An ancient Greek mathematician credited with the theorem, though the relationship was known to earlier civilizations like the Babylonians.
- What is a Pythagorean triple?
- A set of three whole numbers that fit the theorem, like 3-4-5 or 5-12-13.
- Can it be used on any triangle?
- No — only right triangles. For other triangles you'd use the law of cosines, a more general version.