`a)VT=-(23-x)+33`
`=-23+x+33`
`=x+10=VP` (đpcm)
Vậy `-(23-x)+33=x+10`
`b)VT=-(a-b)+(b-c)-(a-c)`
`=-a+b+b-c-a+c`
`=(-a-a)+(b+b)+(-c+c)`
`=-2a+2b`
`=2b-2a=VP` (đpcm)
Vậy `-(a-b)+(b-c)-(a-c)=2b-2a`
`c)-(-a+b+c)+(b+c-1)`
`=a-b-c+b+c-1`
`=-(b-a)-(1-b)+(-c+c)`
`=-(b-a)-(1-b)=VP` (đpcm)
Vậy `-(-a+b+c)+(b+c-1)=-(b-a)-(1-b)`