## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$$c^2=a^2+b^2-2ab \cdot\cos{C} \\ b^2=a^2+c^2-2ac \cdot\cos{B}\\ a^2=b^2+c^2-2bc\cdot \cos{A} \\$$
$$c^2=a^2+b^2-2ab \cdot\cos \ C$$ It can also be represented as: $$a^2=b^2+c^2-2bc\cdot\cos \ A \\ b^2=a^2+c^2-2ac \cdot\cos \ B$$