Let 

 

Take natural logs of both sides:



Use the fact that 

 

Use the fact that  to rewrite the last term:





Now finally we can take the derivative implicitly.  

1. We use  to take the 
derivative of the term on the left.

2.  is a constant so its derivative is 0.

3. We use  for the last term

So for  we take the derivatives:





Multiply both sides by 



Use  to replace 



Rearranging the factors:



Replace  by 



Edwin