this is really going to be long.......... by using long division:
x^4 +7x³ -2x² -9x -3
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x+8 I x^5 +15x^4 +54x³ -25x² -75x -34
x^5 +8x^4
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7x^4 +54x³
7x^4 +56x³
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-2x³ -25x²
-2x³ -16x²
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-9x² -75x
-9x² -72x
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-3x -34
-3x -24
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-10
so the result is (x^4+7x³-2x²-9x-3) and -10/((x+8)