reduction formulas In trigonometry, the equations that express sine, cosine and tangent functions of an angle of any size in terms of the functions of an acute angle. For example: sin(90° + x) = cosx sin(180° + x) = -sinx sin(270° + x) = -cosx cos(90° + x) = -sinx tan(90° + x) = -cotx

Related Term: addition formula