Question

若s+y+z=-2,xy+yz+xz=1,则x的2次方+y的2次方+z的2次方的值是

Answer 1

x+y+z=-2 （x+y+z）²=4 x²+y²+z²+2（xy+yz+xz）=4 又∵xy+yz+xz=1

∴ x²+y²+z²=2