Answer: 1-cosA.
- A 1-cosA
- B 1+cosA
- C cosA
- D sinA
Correct answer: A. 1-cosA
Explanation: sin²A = 1 - cos²A = (1-cosA)(1+cosA). So sin²A/(1+cosA) = (1-cosA)(1+cosA)/(1+cosA) = 1-cosA.
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