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:

What you can do with the Pythagorean Theorem

Find a missing side of a right triangle.

Enter your values or describe the problem in the calculator above. Review the result and the explanation before using it in homework, study or practical calculations.

Example input

e.g. hypotenuse of a right triangle with legs 9 and 12

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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