SAT Math Multiple Choice Practice Question 81: Answer and Explanation

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Question: 81


Which of these three triangles must be a right triangle? (Figures are not drawn to scale.)

A. I only
B. II only
C. I and III
D. II and III
E. I, II, and III

Correct Answer: D


D. Triangle I looks like a right triangle, but the diagram doesn't provide any actual evidence that it is. Triangle II, on the other hand, has two angles that add up to 90°, so the third angle must be 90°. Triangle III has sides of 5, , and 6. You can test whether this triangle is right by using the Pythagorean Theorem: , which is 62, so Triangle III is a right triangle, too.

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