x+y+z=a
(x+y+z)^2=a^2
(x+y+z)^2=x^2+y^2+z^2+2(xy+yz+zx)
x^2+y^2+z^2=(x+y+z)^2-2(xy+yz+zx)=a^2-2b
已知x+y+z=a ,xy+yz+zx=b ,求x2+y2+z2
已知x+y+z=a ,xy+yz+zx=b ,求x2+y2+z2
2代表平方
2代表平方
数学人气：419 ℃时间：2019-11-09 19:31:01
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