Pythagorean Theorem

Find the hypotenuse or a missing leg of a right triangle using a² + b² = c², with the substitution and square root shown. Try “hypotenuse of a right triangle with legs 9 and 12”.

Try an example:

How the Pythagorean Theorem works

  1. Label the hypotenuse c (opposite the right angle) and the legs a and b.
  2. Substitute: 9² + 12² = 81 + 144 = 225.
  3. Take the square root of both sides: c = 15.

Frequently asked questions

When can I use the Pythagorean theorem?

Only for right triangles, to relate the two legs and the hypotenuse.

What are Pythagorean triples?

Whole-number sets that fit a² + b² = c², such as 3-4-5, 5-12-13 and 8-15-17.

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