Solving for a variable in the partial derivative of a summation

[bpk356]

I'm trying to find the partial derivative of Q with respect to w₀ and then set it equal to 0 and solve for w₀. Finding the partial derivative was easy, but once I've got it, I'm having a hard time getting w₀ by itself. Here's the original equation:

$$Q(w_{0},w_{1},w_{2},w_{3})=\sum\left(y_{i} - w_{2}\frac{1}{1+e^{x_{i}w_{0}+w_{1}}} - w_{3}\right)^{2}$$

 

[bpk356]

Here's the partial derivative:
[tex][/tex]
[tex][/tex]

I can't get the LaTeX right...