# Law o cosines

Figur 1 – A triangle. The angles α (or A), β (or B), an γ (or C) are respectively opposite the sides a, b, an c.

In trigonometry, the law o cosines (an aa kent as the cosine formula or cosine rule) relates the lenths o the sides o a triangle tae the cosine o ane o its angles. Uisin notation as in Fig. 1, the law o cosines states

${\displaystyle c^{2}=a^{2}+b^{2}-2ab\cos \gamma \,}$

whaur γ denotes the angle conteened atween sides o lenths a an b an opposite the side o lenth c.