Answer
`a,`
`-b - (b - a + c)`
`= -b - b + a - c`
`= (-b - b) + a - c`
`= -2b + a - c`
____________________
`b,`
`-(a - b + c) - (c - a)`
`= -a + b - c - c + a`
`= (-a + a) + b - (c + c)`
`= b - 2c`
_____________________
`c,`
`b - (b + a - c)`
`= b - b - a + c`
`= (b - b) - a + c`
`= -a + c`
`= c - a`
_________________
`d,`
`a - (-b + a - c)`
`= a + b - a + c`
`= (a - a) + b + c`
`= b + c`
$\text{Quy tắc đổi dấu}$
$\bullet$ `-` $\text{với}$ `-` $\text{bằng}$ `+`
$\bullet$ `-` $\text{với}$ `+` $\text{bằng}$ `-`
$\bullet$ `+` $\text{với}$ `+` $\text{bằng}$ `+`
$\bullet$ `+` $\text{với}$ `-` $\text{bằng}$ `-`
