Question 626015
<pre>
{{{(n^2 - 10n + 24)/(n^2 - 13n + 42)}}}  -  {{{9^""/(n^"" - 7)}}}

Factor the numerator and denominator of the first fraction:

{{{((n-6)(n-4))/((n-7)(n-6))}}}  -  {{{9/(n - 7)}}}

Cancel the (n-6)'s in the first fraction:

{{{((cross(n-6))(n-4))/((n-7)(cross(n-6)))}}}  -  {{{9/(n - 7)}}}

{{{(n-4)/(n - 7)}}} - {{{9/(n - 7)}}}

Wow! We didn't even need to get the LCD because it already has the LCD.
We combine the two numerators over the LCD:

{{{(n-4-9)/(n - 7)}}}

{{{(n-13)/(n - 7)}}}

Edwin</pre>