Phá ngoặc rồi viết gọn
1 , a - ( a - b - c ) - ( b - c -a ) - ( c - b -a )
2 , - ( a + b + c ) - ( b - c -a ) + ( 1 - a - b ) - ( c - 3b )
3 , ( b - c - 6 ) - ( 7 - a + b ) + c
4 , - ( 3b - 2a - c ) - ( a - b - c ) - ( a - 2b -+ 2c )
5 , ( 4a - 3b + 2c ) - ( 4b - 3c - 2a ) - ( 4c - 3a + 2b ) + ( a - b ) - c
6, 2a - { a - b [ a - b - ( a + b + c ) + 2b ] - c - b }