# SAT Math Multiple Choice Practice Question 81: Answer and Explanation

### Next steps

- Use your browser's back button to return to your test results.
- Do another SAT math multiple choice practice tests.

**Question: 81**

**15.**

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

**Explanation:**

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.