-c^2 + c*(d - c - 9.0/c - 9.0/d)/d
3 3 / / 2 \\ - c *d + c*d*\-9*d + c*\-9 + d - c*d// ---------------------------------------- 3 c*d
/ 2 \ 2 2 -9*d + c*\-9 + d - c*d/ - c *d -------------------------------- 2 d
/ 2 2 2 2\ -\9*c + 9*d + d*c + c *d - c*d / ----------------------------------- 2 d