Answer: 12/13.
- A 5/12
- B 12/13
- C 13/12
- D 5/13
Correct answer: B. 12/13
Explanation: Using sin²A + cos²A = 1: cos²A = 1 - 25/169 = 144/169, cos A = 12/13.
Unit circle with standard angles 0, 30, 45, 60, 90 degrees; at 45 degrees the point is (cos45, sin45) = (1/sqrt2, 1/sqrt2).
Concept context
Ratios, identities, and applications in triangles