What is the length of the hypotenuse, x, if (20, 21, x) is a Pythagorean triple?

In a Pythagorean triple, the two smaller numbers are the legs and the hypotenuse satisfies a² + b² = x². So x² = 20² + 21² = 400 + 441 = 841, and x = 29. The hypotenuse is 29, choice B.

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