Question 1063876
 Please describe and correct the error.
<pre>
   {{{((r^2 -7r +12)/(r+4))  /  ((r^2 -7r + 12) / (r^2 + 6r + 8))}}} <--given

 = {{{( ((r - 3)(r - 4))/(r+4))  /  (((r-4)(r-3))/((r+2)(r+4)))}}} <--correct

 ={{{cross(((r+4)/((r-3)(r-4)))*  (((r-4)(r-3))/((r+2)(r+4))))}}} <--incorrect, which led to incorrect answer  ={{{cross(1/(r+2))}}} 

To divide the first fraction by the second fraction, we must 
invert the SECOND fraction and change the division to multiplication.
The error here was to invert the FIRST fraction.  

From here:

{{{( ((r - 3)(r - 4))/(r+4))  /  (((r-4)(r-3))/((r+2)(r+4)))}}}

Inverting the SECOND fraction and changing the division to
multiplication gives:

{{{( ((r - 3)(r - 4))/(r+4))  *  (((r+2)(r+4))/((r-4)(r-3)))}}} 

Now everything cancels but this:

{{{r+2}}}  <-- correct answer.

Edwin</pre>