Answer: Both B and C.
- A 1
- B cos 2θ
- C 2cos²θ - 1
- D Both B and C
Correct answer: D. Both B and C
Explanation: cos²θ - sin²θ = cos 2θ. Also cos 2θ = 2cos²θ - 1. So B and C are equal expressions.
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