The sides of a triangle have lengths of x, x + 5, and 25. If the longest side is 25, which of the following values of x would make the triangle right?

Since 25 is the longest side, it must be the hypotenuse of the right triangle. Apply the Pythagorean theorem: x² + (x + 5)² = 25², which simplifies to x² + 5x − 300 = 0. Factoring gives (x + 20)(x − 15) = 0, so the positive value is x = 15. The correct choice is 15.

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