BC = a, AC = b and AB = c Area of triangle is denoted by Δ and the radius of the circumcircle by R. Sine Rule : Cosine Rule : $latex \begin{array}{*{35}{l}} {} & \cos A=\frac{{{b}^{2}}+{{c}^{2}}-{{a}^{2}}}{2bc} \\ {} & \cos B=\frac{{{c}^{2}}+{{a}^{2}}-{{b}^{2}}}{2ca} \\ {} & \cos C=\frac{{{a}^{2}}+{{b}^{2}}-{{c}^{2}}}{2ab} \\ \end{array}$ Projection Formulae: a = b […]