当m为何值时 x³+y³+z³+mxyz能被x+y+z整除
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当m为何值时 x³+y³+z³+mxyz能被x+y+z整除
可以这样想,就是设法提出x+y+z出来,采用降次的方法,
x^3+y^3+z^3
=x^2(x+y+z)+y^2(x+y+z)+z^2(x+y+z)-x^2(y+z)-y^2(x+z)-z^2(x+y)
=(x^2+y^2+z^2)(x+y+z)-x^2(y+z)-y^2(x+z)-z^2(x+y)
=(x^2+y^2+z^2)(x+y+z)-[xy(x+y+z)+xz(x+y+z)+yz(x+y+z)-3xyz]
=(x^2+y^2+z^2)(x+y+z)-(xy+xz+yz)(x+y+z)+3xyz
故当m=-3时,代数式能被x+y+z整除
再问: 不是m=3吗?
再答: x^3+y^3+z^3这个式子等于(x^2+y^2+z^2)(x+y+z)-(xy+xz+yz)(x+y+z)+3xyz
而题目是x³+y³+z³+mxyz=(x^2+y^2+z^2)(x+y+z)-(xy+xz+yz)(x+y+z)+(m+3)xyz
x^3+y^3+z^3
=x^2(x+y+z)+y^2(x+y+z)+z^2(x+y+z)-x^2(y+z)-y^2(x+z)-z^2(x+y)
=(x^2+y^2+z^2)(x+y+z)-x^2(y+z)-y^2(x+z)-z^2(x+y)
=(x^2+y^2+z^2)(x+y+z)-[xy(x+y+z)+xz(x+y+z)+yz(x+y+z)-3xyz]
=(x^2+y^2+z^2)(x+y+z)-(xy+xz+yz)(x+y+z)+3xyz
故当m=-3时,代数式能被x+y+z整除
再问: 不是m=3吗?
再答: x^3+y^3+z^3这个式子等于(x^2+y^2+z^2)(x+y+z)-(xy+xz+yz)(x+y+z)+3xyz
而题目是x³+y³+z³+mxyz=(x^2+y^2+z^2)(x+y+z)-(xy+xz+yz)(x+y+z)+(m+3)xyz
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