Unit circle: (cos θ, sin θ) for angle θ. Radius = 1.
Key angles (radians): 0, π/6, π/4, π/3, π/2, π, 3π/2, 2π.
sin²θ + cos²θ = 1 | 1+tan²θ = sec²θ | 1+cot²θ = csc²θ
sin(A±B) = sinA·cosB ± cosA·sinB
cos(A±B) = cosA·cosB ∓ sinA·sinB
sin(2A) = 2sinA·cosA | cos(2A) = cos²A − sin²A
📌 Memorize — ASTC Rule (All Students Take Calculus)
Q1: All positive | Q2: Sin+ | Q3: Tan+ | Q4: Cos+
Period of sin/cos = 2π | Period of tan = π
Example: sin(π/6) = 1/2, cos(π/3) = 1/2, tan(π/4) = 1