Correct Answer: Option A — (tan A + tan B)/(1 - tan A·tan B)
Explanation:
tan(A+B) = (tan A+tan B)/(1-tan A·tan B). This compound angle formula is derived from sin(A+B)/cos(A+B). Compound angle formulas for sin cos and tan are essential for solving equations and proving identities. They appear in CSS PMS and engineering entrance exams requiring higher trigonometric manipulation.