13.14.15.16.
17.
18.19.
20.21.22.23.24.
25.26.27.TRIGONOMETRY
BASIC IDENTITIESsin^2 θ + cos^2 θ = 1.1 + tan^2 θ = sec^2 θ.1 + cot^2 θ = csc^2 θ.
SUM AND DIFFERENCE FORMULAS
sin (α ± β) = sin α cos β ± cos α sin β.
cos (α ± β) = cos α cos β sin α sin β.DOUBLE-ANGLE FORMULAS
sin 2α = 2 sin α cos α.cos 2α = cos^2 α − sin^2 α = 2 cos^2 α − 1 = 1 − 2 sin^2 α.HALF-ANGLE FORMULASREDUCTION FORMULAS
sin (−α) = −sin α: cos (−α) = cos α.sin (π − α) = sin α; cos (π − α) = −cos α.