Length_of_Angle_Bisector

Let $\triangle ABC$ be a triangle. Let $AD$ be the angle bisector of $\angle BAC$ in $\triangle ABC$. 300px Let $d$ be the length of $AD$. Then $d$ is given by $d^2 = \dfrac {b c} {\paren {b + c}^2} \paren {\paren {b + c}^2 - a^2}$ where $a$, $b$, and $c$ are the sides opposite $A$, $B$ and $C$ respectively.