C.2 Circular Measure and Trigonometric Identities

Radian measure (the natural angular unit), arc length s = rθ, sector area A = ½r²θ. Unit-circle definitions of sin θ (y-coordinate), cos θ (x-coordinate), tan θ = sin θ / cos θ — generalising right-triangle ratios to ANY angle. Exact values for special angles 0, π/6, π/4, π/3, π/2 with quadrant sign rules (ASTC). Pythagorean identity sin²θ + cos²θ = 1 and double-angle identities for sin 2θ and cos 2θ.