O-Level Additional Mathematics: Trigonometric Identities & Equations

Trigonometric identities

Core: sin²θ + cos²θ = 1, 1 + tan²θ = sec²θ. Use double-angle (sin2θ, cos2θ) and compound-angle (sin(A±B)) identities to simplify.

Proof tips

Always start from one side, use expansions, and convert everything to sin/cos if stuck.

Exam habits

• Memorise exact values (30°, 45°, 60°).
• Watch out for domain restrictions when solving trig equations.
• Show all steps in proving identities.