Question

x-y-z=3 yz-xy-xz=3 则x2+y2+z2=

Answer 1

x-y-z=3 yz-xy-xz=3

(x-y-z)^2=x^2+y^2+z^2+2yz-2xz-2xy=x^2+y^2+z^2+2(yz-xy-xz)=x^2+y^2+z^2+6=9

所以x^2+y^2+z^2=3