I'll give you the format of the question, and you just have to look at it carefully.

1. Solution: Because A and B are reciprocal,

So a+b=0.

So a+b 0

—— =——=0

20 10 20 10

2. Solution: Because A and B are opposites,

So a+b=0.

Derived from the distribution law,

3a-a+3b=3(a+b)-a

=0-a

=-a or =b