Question

(a+3)^3-(a-1)^3-12a^2

Answer 1

$=(a+3-(a-1))((a+3)^2+(a+3)(a-1)+(a-1)^2)-12a^2= \ =4(a^2+6a+9+a^2+2a-3+a^2-2a+1)-12a^2= \ = 4(3a^2+6a+7)-12a^2=24a+28$