已知x-y=y-z=3/5,x²+y²+z²=1,则xy+yz+xz=?
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已知x-y=y-z=3/5,x²+y²+z²=1,则xy+yz+xz=?
已知x-y=y-z=3/5,x²+y²+z²=1,则xy+yz+xz=?
已知x-y=y-z=3/5,x²+y²+z²=1,则xy+yz+xz=?
x-y=3/5
y-z=3/5,
两式相加得
x-z=6/5
(x-y)²+(y-z)²+(x-z)²
=2(x²+y²+z²)-2(xy+yz+xz)
=2-2(xy+yz+xz)
又(x-y)²+(y-z)²+(x-z)²=(3/5)²+(3/5)²+(6/5)²=54/25
2-2(xy+yz+xz)=54/25
xy+yz+xz=-2/25