Выражение (a-8) (a^2+3a+-8a+a^2) (a-3)=

(a-8) (a^2+3a+5)-(5-8a+a^2) (a-3)=

=a^3+3a^2+5a-8a^2-24a-40-(5a-15-8a^2+24a+a^3-3a^2)=

=a^3+3a^2+5a-8a^2-24a-40-(29a-15-11a^2+a^3)=

=a^3+3a^2+5a-8a^2-24a-40-29a+15+11a^2-a^3=

=6a^2-48a-25.

(a-8) (a^2+3a+5)-(5-8a+a^2) (a-3) = a^3-8a^2+3a^2-24a+5a-40-(5a-8a^2+a^3-15+24a-3a^2) = a^3-5a^2-19a-40+11a^2-a^3-29a+15=6a^2-48a-25