The compound angle formulas express trig functions of (A +/- B) in terms of functions of A and B individually. The six core formulas are: sin(A+B) = sinAcosB + cosAsinB, sin(A-B) = sinAcosB - cosAsinB, cos(A+B) = cosAcosB - sinAsinB, cos(A-B) = cosAcosB + sinAsinB, tan(A+B) = $\frac{tanA + tanB}{(1 - tanAtanB)}$, tan(A-B) = $\frac{tanA - tanB}{(1 + tanAtanB)}$. These formulas are derived from the unit circle rotation or the distance formula. They serve as the foundation for double angle formulas (set B = A), triple angle formulas, and product-to-sum transformations. In JEE, compound angle formulas are tested both directly (compute sin 75 degrees) and indirectly (simplify expressions where compound angles appear). The key to fluency is practice — these must be recalled instantly without derivation during the exam.