Question 178160
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{{{(x/(x^2-2x-3)) - (3x/(x^2-9))}}}
Factor the DENs
={{{(x/((x-3)*(x+1))) - 3x/((x-3)*(x+3))}}}
To get a common DEN, multiply the 1st one by (x+3) and the 2nd by (x+1).  Multiply NUM and DEN.
={{{(x*(x+3)/((x-3)*(x+1)*(x+3))) - 3x*(x+1)/((x-3)*(x+3)*(x+1))}}}
Now the DENs are the same, so add the NUMS after expanding them.
={{{(x^2+3x)/((x-3)*(x+1)*(x+3)) + (-3x^2-3x)/((x-3)*(x+3)*(x+1))}}}
={{{(x^2+3x -3x^2-3x)/DEN}}} save some typing
={{{-2x^2/DEN}}}