# cosines law

Let $a$, $b$, $c$ be the sides of a triangle and $A$ the angle opposite to $a$. Then

 $a^{2}=b^{2}+c^{2}-2bc\cos A.$

Remark.  Cosines law is the generalised form of Pythagorean theorem, which latter concerns only the right triangles.

 Title cosines law Canonical name CosinesLaw Date of creation 2013-03-22 11:42:35 Last modified on 2013-03-22 11:42:35 Owner drini (3) Last modified by drini (3) Numerical id 26 Author drini (3) Entry type Theorem Classification msc 51M04 Classification msc 05A15 Classification msc 05A10 Classification msc 05A16 Synonym law of cosines Related topic SinesLaw Related topic PythagorasTheorem Related topic DerivationOfCosinesLaw Related topic CosinesLaw Related topic StewartsTheorem Related topic AlternativeProofOfTheSinesLaw Related topic SinesLawProof Related topic ProofOfStewartsTheorem