Bài `1:`

`a)`

 Ta có:

`534 + 1266 = 1800`

`635 + 1167 = 1802`

   `=> 1800 < \overline{x80x} < 1802`

   `=> \overline{x80x} = 1801 => x = 1`(thỏa mãn cả hai `x` đều bằng nhau)

         Vậy: `x = 1`

`b)` 

 Ta có:

`\overline{x x} + \overline{x x} = 2 . \overline{x x}`

    `=> 197 < 2 . \overline{x x} < 199`

    `=> 2 . \overline{x x} = 198`

    `=> \overline{x x} = 198 : 2 = 99 => x = 9`(thỏa mãn cả hai `x` đều bằng nhau)

         Vậy: `x = 9`

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