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``}`.
