Question 153544
Simplify the expression (x^2 - 9)/(x^2 + 3x)

My attempt to this problem was to cancel out the x^2 because they divided each other, and then i simplified -9/3x to -3x. But when i check to see if my work is correct by substituting x for 2, the answers did not match.
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You may only cancel "factors" that are common to the numerator and to the
denominator.
x^2 is a "term" in the numerator and a "term" in the denominator and 
may not be cancelled.
Example (2 + 3)/(2 + 5)
If you cancelled the "2" you would get 3/5; but the answer should be 5/7.
Don't cancel terms.
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Simplify the expression (x^2 - 9)/(x^2 + 3x)
Factor where you can to get:
[(x-3)(x+3)] / [x(x + 3)] 
Notice that the (x+3) is a factor of the numberator and of the denominator
so you may cancel it to get:
 = (x-3)/(x)
Notice that you cannot cancel the "x" because it is a "term" and not a factor in the numerator.
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Cheers,
Stan H.