Question

what should be added to 1+2x-3x2to get x2-x-1

Answer 1

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Here is your answer

Let the number added is y

ATQ
$y + 1 + 2x - 3 {x}^{2} = {x}^{2} - x - 1 \\ \\ y = {x}^{2} - x - 1 - 1 - 2x + 3 {x}^{2} \\ \\ y = 4 {x}^{2} - 3x - 2$
Therefore We add this is
$4 {x}^{2} - 3x - 2$

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