Look at the image attached: It shows the differentiation of a rational function using

Wolfram Alpha.

I am having difficulties understanding why the final calculation of the derivative is equal to:

$\displaystyle -\frac{\7}{\ 2(x-2)^2} $

*Note: The final solution is not shown on the image attached.

The entire thing can be viewed here:

http://www.wolframalpha.com/input/?i=Derivative+Calculator&f1=%28x%2B5%29%282x-4%29^-1&f=Derivative.derivativefunction_%28x%2B5%29%28 2x-4%29^-1&a=*FVarOpt-_**Derivative.derivativevariable--

Looking at the steps in the image attached, I understand everything that's happening up until the final line.

From my interpretation it seems it should be:

$\displaystyle \frac {\1(2x-4)-2(x+5)(1)}{\2(x-2)^2}$

= $\displaystyle \frac {2x-4-2x-10}{\(2x-4)^2}$

which:

=$\displaystyle -\frac {\14}{\(2x-4)^2}$

Where is the -7 coming from? What steps am I missing and what am I doing wrong?