1) a-b+c-d-c+d+b-a =  0

2)-a+b-c-d-b+a-c+d = -2c

3)a-b-c-a+d+d-b+c = -2b+2d

4)-c+b+d+a-b-c-d+a = -2c+2a

(c) din9n9

1) a-b+c-d-c+d+b-a =  0

2)-a+b-c-d-b+a-c+d = -2c

3)a-b-c-a+d+d-b+c = -2b+2d

4)-c+b+d+a-b-c-d+a = -2c+2a

КАК-то так