2 2 3*c - 3*d
3*c^2 - 3*d^2
1*(c + d)*(c - d)
(1*(c + d))*(c - d)
3.0*c^2 - 3.0*d^2
3*(c + d)*(c - d)
/ 2 2\ 3*\c - d /
3*(c^2 - d^2)