问题 解答题

已知A=x3+3x2y-5xy2+6y3-1,B=y3+2xy2+x2y-2x3+2,C=x3-4x2y+3xy2-7y3+1.求证:A+B+C的值与x、y无关.

答案

A+B+C=(x3+3x2y-5xy2+6y3-1)+(y3+2xy2+x2y-2x3+2)+(x3-4x2y+3xy2-7y3+1)

=(1+1-2)x3+(3+1-4)x2y+(-5+2+3)xy2+(6+1-7)y3-1+2+1

=2.

故A+B+C的值与x,y无关.

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