The vertices of ΔRST are R(–1,–1), S(–1,11) and T(4,11). Which could be the side lengths of a triangle that is similar but not congruent to ΔRST?

The vertical side RS is 12 units, and the horizontal side ST is 5 units. By the Pythagorean theorem, RT = √(12² + 5²) = 13 units, so the side lengths are 5, 12, and 13. A similar triangle must have all three side lengths multiplied by the same scale factor; choice C gives 10, 24, and 26, which are twice the original lengths, so it is similar but not congruent.

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