Law of Cosines
$$a^{2} = b^{2} + c^{2} - 2bc \cos(A)$$ $$b^{2} = a^{2} + c^{2} - 2ac \cos(B)$$ $$c^{2} = a^{2} + b^{2} - 2ab \cos(C)$$ also $$\frac{a}{\sin A} = \frac{b}{\sin{B}} = \frac{c}{\sin C}$$
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