(3a+10)(a-4)-(4a^2-5a)=(3а^2-12a+10a-40)-(4a^2-5a)=(3а^2-2a-40)-(4a^2-5a)=3а^2-2a-40-4a^2+5a= -a^2+3a-40
(3a+10)(a-4)-(4a^2-5a)=(3а^2-12a+10a-40)-(4a^2-5a)=(3а^2-2a-40)-(4a^2-5a)=3а^2-2a-40-4a^2+5a= -a^2+3a-40