SAT Math Multiple Choice Practice Question 79: Answer and Explanation

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Question: 79

13. Find the perimeter of a square whose diagonal has length m.

A. 6 m
B. m
C. 24 m
D. m
E. 48 m

Correct Answer: C


C. Here's the square with the diagonal drawn:

Hopefully, you recognize that the triangles in this drawing are both 45-45-90 triangles. So the hypotenuse — which is also the diagonal of the square — equals a leg times . Because the legs are just the sides of the square, each leg equals 6 m, and the perimeter is 4 × 6 m = 24 m.

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