chứng tỏ
( a - b + c ) - ( a+ c ) = - b
( a + b ) - ( b - a ) + c = 2a + c
- ( a + b - c ) + ( a - b - c ) = - 2b
a( b + c ) - a(b + d ) = a ( c - d )
a ( b - c ) + a ( d + c ) = a ( b + d)
GIÚP MIK NHA MIK TICK CHO BN NÀO LÀM ĐÚNG
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!