(x + 4) (y - 5); (x - 8) (6 - y);
(a + 3) (a - 4);
(a - 1) (6 - a);
(5a - 7) (3a + 1);
(3b + 7) (4 - 3b);
5 (x + 2) (x + 3);
- 6 (a + 4) ( a - 1)

(x + 4) (y - 5)=ху-5х+4у-4•5=ху-5х+4у-20

(x - 8) (6 - y)=6х-ху-8•6-8•(-у)=6х-ху-48+8у

(a + 3) (a - 4)=ах-4х+3а-3•4=ах-4х+3а-12

(a - 1) (6a)=6а-а^2-6+а=7а-а^2-6=-а^2+7-6

(5a - 7)(3a+1)=15а^2+5а-21а-7=15а^2-16а-7

(3b+7(4-3b)=12b-9b^2+28-21b=-9b-9b^2+28

5 (x + 2) (x + 3)=(5x+10)•

•(x+3)=5x^2+15x+10x+30=5x^2

- 6 (a + 4) ( a - 1)=(-6a-24)•

•(a-1)=-6a^2+6a-24a+24=-6a^2-18a+24