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已知x+y+z+5,且xy+xz+yz=7,求x^2+y^2+z^2的值
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已知x+y+z+5,且xy+xz+yz=7,求x^2+y^2+z^2的值
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题目应是:已知x+y+z=5,且xy+xz+yz=7,求x^2+y^2+z^2的值
(x+y+z)^2 =x^2+y^2+z^2+2xy+2xz+2yz
5^2 =x^2+y^2+z^2+2(xy+xz+yz)
x^2+y^2+z^2=25-2*7
x^2+y^2+z^2=11
(x+y+z)^2 =x^2+y^2+z^2+2xy+2xz+2yz
5^2 =x^2+y^2+z^2+2(xy+xz+yz)
x^2+y^2+z^2=25-2*7
x^2+y^2+z^2=11
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