Answer: sin²θ + cos²θ = 1.
- A sin²θ - cos²θ = 1
- B sin²θ + cos²θ = 1
- C sinθ × cosθ = 1
- D sinθ + cosθ = 1
Correct answer: B. sin²θ + cos²θ = 1
Explanation: sin²θ + cos²θ = 1 for all values of θ. This is the Pythagorean identity.
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