9*y 49*x --- - ---- x y ---------- 3*y - 7*x
(9.0*y/x - 49.0*x/y)/(3.0*y - 7.0*x)
2 2 - 49*x + 9*y ---------------- x*y*(-7*x + 3*y)
3 7 - + - x y
3*y + 7*x --------- x*y