7 - (b+14) - 2b;

3b - (18+b) + 8;

(21-a) - (20-2a) ;

- (13+b) + (-b-13) ;

- (7-x) + 4 (x-5) ;

-9 (y-4) - (12+y) ;

7 - (b+14) - 2b=7-b-14-2b = - 3b-7

3b - (18+b) + 8=3b-18-b+8 = 2b-10

(21-a) - (20-2a) = 21-a-20+2a=1a+1

- (13+b) + (-b-13) = - 13-b-b-13=-2b-26

- (7-x) + 5 (x-5) = - 7+x+5x-25=6x-32

-9 (y-4) - (12+y) = - 9y+36-12-y=8y+24

1) а) 2x - (2x+y) + y = 2x-2x-y+y = 0

б) - a + (2a-b) + 2b = - a+2a-b+2b = а+b

в) 7 - (b+14) - 2b = 7-b-14-2b = - 7-3b

г) 3b - (18+b) + 8 = 3b-18-b+8 = 2 - 10

2) а) 2 (3-x) - (8+x) = 6-2x-8-x = - 2-3x

б) - 4 (y+5) + (12-y) = - 4y-20+12-y = - 5y - 8

в) - (7-x) + 4 (x-5) = - 7+x+4x-20 = 5x-27

г) - 9 (y-4) - (12+y) = - 9y+36-12-y = 24 - 20y