f:{[a;b;c]{x[-b;_sqrt(b^2)-4*a*c]%2*a}'(+;-)}
g:{[a;b;c]((-b)+1 -1*_sqrt(b^2)-4*a*c)%2*a}

g[2;-4;-6]

\

  -b  +/- sqrt(b^2 - 4 * a * c)
  -----------------------------
             2 * a