Question 9293
{{{13/(x^2-16)}}}  and {{{ 7/(x-4) }}}


Notice that the denominator of the first fraction factors so you really have:
{{{13/((x-4)(x+4))}}}  and {{{ 7/(x-4) }}}


The objective is to get the denominators to be the same.  You are allowed to multiply the numerator and denominator of any given fraction by the same quantity.  Can you see that the Least Common Denominator (LCD) is (x-4)(x+4)?


The first denominator HAS the LCD, but the second denominator is missing a factor.  The second denominator is missing a factor of (x+4).  So you must multiply the numerator and denominator of the second fraction by (x+4):  


{{{13/((x-4)(x+4))}}}  and {{{ (7(x+4))/((x-4)(x+4)) }}} or
{{{13/((x-4)(x+4))}}}  and {{{ (7x+28)/((x-4)(x+4)) }}}


R^2 at SCC