Using Geo/Trig on an Algebra Problem

What is $xy+yz+xz$ if $x^2+xy+y^2=1$, $y^2+yz+z^2=2$, and $x^2+xz+z^2=3$?

\(xy+yz+xz \\if\\ x^2+xy+y^2=1, \\y^2+yz+z^2=2, \\x^2+xz+z^2=3\)