Question

what should be added to
$2x {}^{4} y {}^{3 } - x {}^{3} y {}^{2} - 3x {}^{2} y - 4 \: to \: get \: 5x {}^{4} y {}^{3} + 2x {}^{3} y {}^{2} + x {}^{2} y - 9$
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Answer 1

Step-by-step explanation:

$3 {x}^{4} {y}^{3} + 3 {x}^{3} {y}^{2} + 4 {x}^{2} y - 5$