(5x+2x-3-4x^3)-(-x+3x^3-x^2) 合并同类项

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(5x+2x-3-4x^3)-(-x+3x^3-x^2)
=5x+2x-3-4x^3+x-3x^3+x^2
=-7x^3+x^2+8x-3

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=7X-3-4X^3+X-3X^3-X^2=-7X^3-X^2+8x-3

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