Giải thích các bước giải:

Bài `3.`
`a)`
Ta có:
`A=6789.6789`
`A=(6788+1).6789`
`A=6788.6789+6789`
`B=6790.6788`
`B=(6789+1).6788`
`B=6789.6788+6788`
CÓ:
`6788.6789=6789.6788`
`=>6788.6789+6789>6789.6788+6788`
`=>6789.6789>6790.6788`
`=>A>B`
Vậy `A>B`
`b)`
Ta có:
`A=137.454+206`
`A=137.(453+1)+206`
`A=137.453+137+206`
`A=137.453+343`
`B=453.138-110`
`B=453.(137+1)-110`
`B=137.453+453-110`
`B=137.453+343`
Có:
`137.453=137.453`
`=>137.453+343=137.453+343`
`=>137.454+206=453.138-110`
`=>A=B`
Vậy `A=B`

`a)`

Ta có :

`A = 6789 . 6789`

`= 6789 . ( 6788 + 1)`

`= 6789 . 6788 + 6789 . 1`

`= 6789 . 6788 + ( 6788 + 1) . 1`

`= 6789 . 6788 + 6788 . 1 + 1 . 1`

`=6789 . 6788 + 6788 + 1`

`= ( 6789 + 1) . 6788 + 1`

`= 6790 . 6788 +1`

`=> A= 6790 . 6788 + 1`

`B = 6790 . 6788`

Vì `6790 . 6788 + 1`    > `6790 . 6788` 

`=> A > B` 

Vậy `A > B`

``

`b)`

`A = 137 . 454 + 206`

`= 137 . ( 453 + 1) + 206`

`= 137 . 453 + 137 . 1 + 206`

`= 137 . 453 + 137 + 206`

`= 137 . 453 + 343`

`=> A = 137 . 453 + 343`

``

`B = 453 . 138 - 110`

`= 453 . ( 137 + 1) - 110`

`= 453 . 137 + 453 . 1 - 110`

`= 453 . 137 + 453 - 110`

`= 453 . 137 + 343`

`=> B=453 . 137 + 343`

Vì `137 . 453 + 343 = 453 . 137 + 343`

nên `A = B`

Vậy `A = B`

`#caty09`