/ 2 \ (a + 2)*(a + 2)*(a + 4) - a*\a + 20/
2 / 2\ (2 + a) *(4 + a) - a*\20 + a /
(2.0 + a)^2*(4.0 + a) - a*(20.0 + a^2)
2 16 + 8*a