C.4 Reciprocal/Inverse Trig and Compound AnglesHL

HL only. Reciprocal trig ratios sec θ = 1/cos θ, cosec θ = 1/sin θ, cot θ = cos θ/sin θ, and the derived Pythagorean identities 1 + tan²θ = sec²θ and 1 + cot²θ = cosec²θ. Inverse trig functions arcsin, arccos, arctan with their principal-value domains and ranges. Compound-angle identities for sin(A ± B), cos(A ± B), tan(A ± B); double-angle for tan; symmetry properties (evenness/oddness, periodicity); co-function relations like sin(π/2 − θ) = cos θ.