Bài 1: (2 điểm). Thực hiện các phép tính: a) 25.37 + 37.75 b) 128 - 345 + 272 + 345 c) 3⁷ : 3⁵ - 2⁸ : 2⁶ - 5.2019⁰ d) 1 + 3 + 5 + ... + 25 Bài 2: (2 điểm). Tìm x biết a) 17 - x = 25 b) 20 - (73 - x) = 47 c) 2x-3 = 32 d) |2 - x| = 7

Bài 1:

`a``)` `25``.``37` `+` `37``.``75`

`=` `37``.``(``25``+``75``)`

`=` `37``.``100`

`=``3700`

`b``)` `128``-``345``+``272``+``345`

`=` `(``128``+``272``)``+``(``-``345``+``345``)`

`=``400``+``0`

`=``400`

`c``)` `3⁷` `:``3⁵``-``2⁸``:``2⁶``-``5``.``2019⁰`

`=``3²``-``2²``-``5``.``1`

`=``9``-``4``-``5`

`=``9``-``(``4``+``5``)`

`=``9``-``9`

`=``0`

`d``)` `1``+``3``+``5``+``...``+``25`

`=` `(``1``+``25``)``+``(``3``+``23``)``+``(``5``+``21``)``+``......``+``(``25``+``1``)`

`=``26``+``26``+``...``+``26`

`=``(``26``.``13``)``:``2`

`=``338``:``2`

`=``169`

Bài 2:

`a``)``17``-``x``=``25`

`x``=``17``-``25`

`x``=``-8`

`b``)` `20``-``(``73``-``x``)` `=` `47`

`73``-``x``=``20``-``47`

`73``-``x``=``-``27`

`x``=``73``-``(``-``27``)`

`x``=``100`

`c``)` `2``x``-``3``=``32`

`2``x``=``32``+``3`

`2``x``=``35`

`x``=``35:2`

`x``=``17,5`

`d``)` |`2``-``x`|`=``7`

`⇒` `2``-``x``=``7` hoặc `2``-``x``=``-``7`

* `2``-``x``=``7`

`x``=``7``+``2`

`x``=``9`

* `2``-``x``=``-``7`

`x``=``(``-``7``)``+``2`

`x``=``5`

Vậy `x` `∈` `{``9` `;` `5``}`.