-12/5-13/8,b 21/17--4/8,c-3/5+7/21+-4/5+7/5

Đáp án:

$a)\,\dfrac{-12}5-\dfrac{13}8\\=\dfrac{-96}{40}-\dfrac{65}{40}\\=\dfrac{-161}{40}\\b)\,\dfrac{21}{17}-\dfrac{-4}8\\=\dfrac{21}{17}+\dfrac48\\=\dfrac{21}{17}+\dfrac12\\=\dfrac{59}{34}\\c)\,\dfrac{-3}5+\dfrac7{21}+\dfrac{-4}5+\dfrac75\\=\dfrac{-3}5+\dfrac{-4}5+\dfrac75+\dfrac7{21}\\=0+\dfrac13\\=\dfrac13$

Giải thích các bước giải:

Đáp án:

 `=-161/40`

`=59/34`

`=1/3`

Giải thích các bước giải:

 `a)``(-12)/5-13/8`

`=-96/40-65/40`

`=(-96-65)/40`

`=-161/40`

`b)``21/17- (-4)/8`

`=21/17+1/2`

`=42/43+17/34`

`=59/34`

`c)``-3/5+7/21+(-4)/5+7/5`

`=-3/5+((-4))/5+7/5+1/3`

`=(-7/5+7/5)+1/3`

`=0+1/3`

`=1/3`

`#Sam`