已知x+y+z=5,xy+yz+xz=7,则x^2+y^2+z^2等于?
问题描述:
已知x+y+z=5,xy+yz+xz=7,则x^2+y^2+z^2等于?
答
(x+y+z)^2=x^2+y^2+z^2+2(xy+yz+xz)=25
x^2+y^2+z^2=25-14=11