-(3x平方y+10x立方)+3x立方+6x立方y+3x平方y-（6x立方y-7x立方）=-3x²y-10x³+3x³+6x³y+3x²y-6x³y+7x³=(-3x²y+3x²y)+(6x³y-6x³y)+(3x³+7x³-10x
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