##  [Law of Cosines](/law-cosines) 

  ##  [Law of Cosines](https://puremath.quantumdictionary.io/law-cosines-0) 

  

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**Pure Mathematics Dictionary**

 







 

 

 

 



 

 

 

 

Definition

For any triangle with side lengths a, b, c and opposite angles α, β, γ respectively, the law of cosines relates a side to the other two and the cosine of the included angle: c^2 = a^2 + b^2 − 2ab cos(γ).