1) (a – b) + (c – d)=a-b+c-d
2)- (-a + b) – (- c – d)=a-b+c+d
3) (a + b) – (c + d)=a+b-c-d
4) –(a + b) + (- c – d)=-a-b-c-d
5) – (a – b) – (c + d)=-a+b-c-d
6) (a – b) - (c – d)=a-b-c+d
7)- (-a - b) + (- c – d)=a+b-c-d
8) (a + b) + (- c + d)=a+b-c+d
9) –(a - b) + (-c – d)=-a+b-c-d
10) – (a + b) – (c + d)=-a-b-c-d