### Basic Rules :

In a triangle ABC, the angles are denoted by capital letters A,B, and C and the lengths of the sides opposite to these angles are denoted by small letters a, b, and c respectively. Semi – perimeter of the triangle is written as s = (a + b + c)/2 and its area denoted by S or Δ . |

**Sine rule: **

, where R is the radius of the circumcircle of the Δ ABC.

**Cosine rule:**

**Projection rule:**

a = b cosC + c cosB ,

b = c cosA + a cosC ,

c = a cosB + b cosA

**Napier’s analogy :**