The theorem
In a right triangle, the square of the hypotenuse (the longest side, opposite the right angle) equals the sum of the squares of the legs: a² + b² = c².
Example
Legs of 3 and 4: c = √(9 + 16) = √25 = 5. A 10 ft ladder with its foot 6 ft from the wall reaches √(100 − 36) = 8 ft up.
Frequently asked questions
Does it work for any triangle?
No, only for right triangles (with a 90° angle). For other triangles, use the law of cosines.
See also
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