What is the length of the hypotenuse, x , if open paren 20 comma 21 comma x close paren is a Pythagorean triple?

In a right triangle, the hypotenuse is the longest side, so use the Pythagorean theorem: x² = 20² + 21² = 400 + 441 = 841. Taking the positive square root gives x = 29, so the correct choice is 29.

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