The rule of removing brackets is: put a "+"sign in front of brackets, and after removing brackets, everything in brackets remains unchanged; Parentheses are preceded by a "-"sign. When the brackets are deleted, all the items in the brackets will change their symbols. For example;

5a+(4 b-3a)-(2 b+a)= 5a+4 b-3a-2 b-a = a+2b。

The rule of parenthesis is: when adding brackets, put a "+"sign in front of the brackets, and everything in the brackets remains unchanged; Parentheses are preceded by a "-"sign, and everything in parentheses changes sign. For example:

4a-3 b-2c = 4a-(3 b+2c)；

7a+2b-5c=7a+(2b-5c)。