已知x+y+z=2,xy+yz+zx=-5,求x²+y²+z²的值
问题描述:
已知x+y+z=2,xy+yz+zx=-5,求x²+y²+z²的值
答
(x+y+z)^2=4
x^2+y^2+z^2+2xy+2xz+2yz=4
x^2+y^2+z^2+2(-5)=4
x^2+y^2+z^2=14