$A(x)=(3x^5 + 3x^2 + 2x^3 + 2x^4 - 7x+5)+(2x^2-3x+3x^5 + 2x^4 +7)
⇔ A(x) = 3x^5 + 3x^2 + 2x^3 + 2x^4 - 7x+5 +2x^2-3x+3x^5 + 2x^4 +7
⇔ A(x) = (3x^5 + 3x^5) + (3x^2 + 2x^2) + 2x^3 + (2x^4 + 2x^4) - 7x + (5+7)$
$⇔ A(x) = 6x^5 + 5x^2 + 2x^3 + 4x^4 - 7x + 12.$
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$B(x)=(3x^5 + 3x^2 + 2x^3 + 2x^4 - 7x+5)-(2x^2-3x+3x^5 + 2x^4 +7)
⇔B(x)=3x^5+3x^2+2x^3+2x^4-7x+5-2x^2+3x-3x^5 - 2x^4 -7
⇔ B(x) = (3x^5 - 3x^5) + (3x^2 - 2x^2) + 2x^3 + (2x^4 - 2x^4) - 7x + (5-7)$
$⇔ B(x) = x^2 + 2x^3 - 7x - 2.$
