Answer :
3x^3 + 7x^2 - 13x - 21
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x + 3
3 7 -13 -21
-3 -9 6 21
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3 -2 -7 0
3x^2 - 2x - 7
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x + 3
3 7 -13 -21
-3 -9 6 21
------------------------------------
3 -2 -7 0
3x^2 - 2x - 7