Expand (a + 2)(3a^2 - 2a - 12)(a^2 - 2a + 1).
(a+2)(3a^2-2a-12)(a^2-2a+1)
=(3a^3-2a^2-12a+6a^2-4a-24)(a^2-2a+1)=(3a^3+4a^2-16a-24)(a^2-2a+1)=3a^5+4a^4-16a^3-24a^2-6a^4-8a^3+32a^2+48a+3a^3+4a^2-16a-24
=3a^5-2a^4-21a^3+12a^2+32a-24
