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.