证明:(x+y+z)3xyz-(yz+zx+xy)3=xyz(x3+y3+z3)-(y3z3+z3x3+x3y3).
来源:学生作业帮 编辑:作业帮 分类:数学作业 时间:2024/05/15 13:17:25
证明:(x+y+z)3xyz-(yz+zx+xy)3=xyz(x3+y3+z3)-(y3z3+z3x3+x3y3).
证明:∵(x+y+z)3xyz-(yz+zx+xy)3=xyz(x3+y3+z3)-(y3z3+z3x3+x3y3)
∴xyz[(x+y+z)3-(x3+y3+z3)]=(yz+zx+xy)3)-(y3z3+z3x3+x3y3)
∴xyz[(x3+y3+z3+3x2y+3xy2+3xz2
+3y2z+3yz2+6xyz)-(x3+y3+z3)],
=(y3z3+z3x3+x3y3+3y2z3x+3z3x2y+3y2zx2+3z2x3y+3zx3y2+6y2z2x2)-(y3z3+z3x3+x3y3),
∴xyz(3x2y+3xy2+3xz2
+3y2z+3yz2+6xyz)=3y2z3x+3z3x2y+3y2zx2+3z2x3y+3zx3y2+6y2z2x2
∴(3x3y2z+3x2y3z+3x2z3y+3y3z2x+3y2z3x+6x2y2z2=3y2z3x+3z3x2y+3y2zx2+3z2x3y+3zx3y2+6y2z2x2
∴(3x3y2z+3x2y3z+3x2z3y+3y3z2x+3y2z3x+6x2y2z2-3y2z3x-3z3x2y-3y2zx2-3z2x3y--6y2z2x2=0
∴(x+y+z)3xyz-(yz+zx+xy)3=xyz(x3+y3+z3)-(y3z3+z3x3+x3y3).
∴xyz[(x+y+z)3-(x3+y3+z3)]=(yz+zx+xy)3)-(y3z3+z3x3+x3y3)
∴xyz[(x3+y3+z3+3x2y+3xy2+3xz2
+3y2z+3yz2+6xyz)-(x3+y3+z3)],
=(y3z3+z3x3+x3y3+3y2z3x+3z3x2y+3y2zx2+3z2x3y+3zx3y2+6y2z2x2)-(y3z3+z3x3+x3y3),
∴xyz(3x2y+3xy2+3xz2
+3y2z+3yz2+6xyz)=3y2z3x+3z3x2y+3y2zx2+3z2x3y+3zx3y2+6y2z2x2
∴(3x3y2z+3x2y3z+3x2z3y+3y3z2x+3y2z3x+6x2y2z2=3y2z3x+3z3x2y+3y2zx2+3z2x3y+3zx3y2+6y2z2x2
∴(3x3y2z+3x2y3z+3x2z3y+3y3z2x+3y2z3x+6x2y2z2-3y2z3x-3z3x2y-3y2zx2-3z2x3y--6y2z2x2=0
∴(x+y+z)3xyz-(yz+zx+xy)3=xyz(x3+y3+z3)-(y3z3+z3x3+x3y3).
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