Bài 1 : Chứng minh đẳng thức : a) -(23-x)+33=x+10 b) -(a-b)+(b-c)-(a-c)=2b-2a c) -(-a+b+c)+(b+c-1)=-(b-a)-(1-b)

`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)`