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C)

`7/19xx5/8xx (-19)/7`

`=7/19xx (-19/7)xx5/8`

`= -1xx5/8`

`=-5/8`

D)

`3/7xx9/11+3/7xx2/11`

`=3/7xx(9/11+2/11)`

`=3/7xx11/11`

`=3/7xx1`

`=3/7`

`8/13+(-9)/17+(-34)/13+(-8)/17`

`=(8/13 + (-34)/13) + (-9/17 + (-8)/17 )`

`= -26/13 + (-17)/17`

`=-2 + (-1)`

`=-3`

`1/3xx3+3:2/3`

`=3/3+3xx3/2`

`=1+9/2`

`=2/2+9/2`

`=11/2`

`B=11/17+ (-8/19) +(-3/4) + 6/17 - 30/19`

`B=(11/17 +6/17) + (-8/19 -30/19) + (-3/4)`

`B= 17/17+(-38/19)+(-3/4)`

`B= 1 +(-2) +(-3/4)`

`B= -1 +(-3/4)`

`B=-7/4`

\(\sqrt[]{\sqrt{ }\dfrac{ }{ }_{ }|^{ }_{ }123456789}\)

điều kiện để \(\dfrac{45}{n+1}\) rút gọn được là :

\(\left(n+1\right)\ne0\) và \(45⋮\left(n+1\right)\)

\(\Leftrightarrow x\ne-1\) và \(\left(n+1\right)\inƯ\left(45\right)\)

mà \(Ư\left(45\right)=\left(\pm1;\pm3;\pm5;\pm9;\pm15\right)\)

\(\Leftrightarrow n\in\left(0;-2;2;-4;4;-6;8;-10;14;-16\right)\)

n+1 chia hết cho Ư(45)

giúp mình với các bạn ! 

50% - 1\(\dfrac{1}{2}\) + \(\dfrac{5}{12}\): 0,5

= \(\dfrac{1}{2}\) - \(\dfrac{3}{2}\) + \(\dfrac{5}{12}\) : \(\dfrac{5}{10}\)

=  - 1 + \(\dfrac{5}{6}\)

= \(-\dfrac{1}{6}\)