In a triangle $ABC$ with usual notations,find the value of $\cot \frac{A}{2} + \cot \frac{B}{2} + \cot \frac{C}{2}$.

• A
  $\frac{s^2}{\Delta}$,where $\Delta$ is the area of the triangle $ABC$.
• B
  $\frac{s}{\Delta}$,where $\Delta$ is the area of the triangle $ABC$.
• C
  $\frac{\Delta}{s}$,where $\Delta$ is the area of the triangle $ABC$.
• D
  $\Delta$,where $\Delta$ is the area of the triangle $ABC$.