已知x+y+z=1,x2+y2+z2=2,x3+y3+z3=3,求xy(x+y)+yz(y+z)+zx(z+x)的值
已知x+y+z=1,x²+y²+z²=2,x³+y³+z³=3,求xy(x+y)+yz(y+z)+zx(z+x)的值
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