Solving Equations

Example: Consider a simultaneous equation system:

$\displaystyle \left\{\begin{array}{ll}

The first function $f_1(x,y)$ is a parabolic cone centrally symmetric to the vertical axis, and its roots form a circle $x^2+y^2=2$ on the x-y plane centered at the origin $(0,\,0)$ with radius $1$; the second function $f_2(x,y)$ is a plane through the origin, and its roots form a straight line $y=C-x$ on the x-y plane. The roots of the equation system are where the two curves intersect: