Answer: 2sinA sinB.
- A 2sinA sinB
- B 2cosA cosB
- C 2sinA cosB
- D 2cosA sinB
Correct answer: A. 2sinA sinB
Explanation: cos(A-B) = cosA cosB + sinA sinB. cos(A+B) = cosA cosB - sinA sinB. Difference = 2 sinA sinB.
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