Trigonometry/For Enthusiasts/Less-Used Trig Identities

Triangle Identities In addition to the Law of Sines, the Law of Cosines, and the Law of Tangents, there are numerous other identities that apply to the three angles A, B, and C of any triangle (where A+B+C=180° and each of A, B, and C is greater than zero). Some of the most notable ones follow: Pythagoras These are all direct consequences of Pythagoras's theorem. Sum/Difference of angles Product to Sum Sum and difference to product , where and Multiple angle These are all direct consequences of the sum/difference formulae Half angle In cases with , the sign of the result must be determined from the value of . These derive from the formulae. Power Reduction Even/Odd Calculus Trigonometric Identities for Triangles Trigonometric Formula Reference