已知x+y+z=5,且xy+xz+yz=7,求x²+y²+z²的值

问题描述:

已知x+y+z=5,且xy+xz+yz=7,求x²+y²+z²的值

x+y+z=5
∴(x+y+z)²=x²+y²+z²+2xy+2xz+2yx=25
∴x²+y²+z²
=25-2(xy+xz+yz)
=25-2×7
=11