Trigonometry/For Enthusiasts/Less-Used Trig Identities
Jump to navigation
Jump to search
Triangle Identities[edit | edit source]
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[edit | edit source]
These are all direct consequences of Pythagoras's theorem.
Sum/Difference of angles[edit | edit source]
Product to Sum[edit | edit source]
Sum and difference to product[edit | edit source]
- , where and
Multiple angle[edit | edit source]
These are all direct consequences of the sum/difference formulae
Half angle[edit | edit source]
In cases with , the sign of the result must be determined from the value of . These derive from the formulae.