\[\frac{{x}^{3}-12{x}^{2}-42}{{x}^{2}+x-3}\]

1
Polynomial Division: Divide x312x242{x}^{3}-12{x}^{2}-42 by x2+x3{x}^{2}+x-3.

xx13-13
x2+x3x^2+x-3x3x^312x2-12x^242-42
x3x^3x2x^23x-3x
13x2-13x^23x3x42-42
13x2-13x^213x-13x3939
16x16x81-81

2
Rewrite the expression using the above.
x13+16x81x2+x3x-13+\frac{16x-81}{{x}^{2}+x-3}

Done

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