Answer: -4/5.
- A 4/5
- B -4/5
- C 3/4
- D -3/4
Correct answer: B. -4/5
Explanation: sin²A + cos²A = 1. cosA = ±4/5. In Q2, cosine is negative. cosA = -4/5.
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