\(\dfrac{a}{\sin A} = \dfrac{b}{\sin B} = \dfrac{c}{\sin C} = 2R\); যেখানে, \(R\) হলো পরিবৃত্তের ব্যাসার্ধ।

1. \(\cos A = \dfrac{b^2 + c^2 - a^2}{2bc} \)
2. \(\cos B = \dfrac{c^2 + a^2 - b^2}{2ca} \)
3. \(\cos C = \dfrac{a^2 + b^2 - c^2}{2ab}\)

1. \(a = b \cos C + c \cos B\)
2. \(b = c \cos A + a \cos C\)
3. \(c = a \cos B + b \cos A\)

1. \(\Delta = \frac{1}{2} bc \sin A = \frac{1}{2} ca \sin B = \frac{1}{2} ab \sin C \)
2. \(\Delta = \sqrt{s(s - a)(s - b)(s - c)}\)
   

   যেখানে, \(s = \frac{a + b + c}{2} =\) অর্ধপরিসীমা