# 5.7 | Law of Cosines

Law of Cosines:
\begin{aligned} a^2 & = b^2 + c^2 -2bc \cos A \\ b^2 & = a^2 + c^2 -2ac \cos B \\ c^2 & = a^2 + b^2 – 2ab \cos C \end{aligned}
Heron’s Area Formula: Given any triangle with sides of length $$a,b,$$ and $$c,$$ the area of the triangle is
$$\text{Area} = \sqrt{s(s-a)(s-b)(s-c)}$$
where $$s = (a+b+c)/2.$$