Đáp án:

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`1) 1/6 - (-5)/6`

`= 1/6 + 5/6`

`= (1+5)/6`

`= 6/6`

`=1`

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`2) 6/13 - (-14)/39`

`= 6/13 + 14/39`

`= 18/39 + 14/39`

`= (18+14)/39`

`= 32/39`

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`3) 4/5 -4/(-18)`

`= 4/5 + 4/18`

`= 46/45`

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`4) 7/21 - 9/(-36)`

`= 7/21 + 9/36`

`= 1/3 + 1/4`

`= 4/12 + 3/12`

`=(4+3)/12`

`= 7/12`

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`5) -12/18- (-21)/35`

`= -12/18 + 21/35`

`= -1/15`

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`6) -3/21 - 6/42`

`= -1/7 - 1/7`

`= [(-1) - 1]/7`

`=-2/7`

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`7) -18/24 - 15/21`

`= -3/4 - 5/7`

`= -41/28`

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`8) 1/6 - 2/5`

`= 5/30 - 12/30`

`= (5-12)/30`

`= -7/30`

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`9) 3/5 - (-7)/4`

`= 3/5 + 7/4`

`= 12/20 + 35/20`

`= (12+35)/20`

`= 47/20`

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`10) (-2) - (-5)/8`

`= (-2) + 5/8`

`= -16/8 + 5/8`

`= [(-16) + 5]/8`

`= -11/8`

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`12) 1/(-8) - (-5)/9`

`= -1/8 + 5/9`

`= -9/72 + 40/72`

`= [(-9) + 40]/72`

`= -31/72`

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`12) 4/13 - [-(-12)]/39`

`= 4/13 + (-12)/39`

`= 4/13 - 12/39`

`= 12/39 - 12/39`

`= (12-12)/39`

`= 0/39`

`= 0`

Giải thích các bước giải:

 

Đáp án `+` Giải thích các bước giải:

\[\begin{array}{l}1,\\\dfrac{1}{6}-\dfrac{-5}{6}\\=\dfrac{1}{6}+\dfrac{5}{6}\\=\dfrac{1+5}{6}\\=\dfrac{6}{6}\\=1\\2,\\\dfrac{6}{13}-\dfrac{-14}{39}\\=\dfrac{6}{13}+\dfrac{14}{39}\\=\dfrac{18}{39}+\dfrac{14}{39}\\=\dfrac{18+14}{39}\\=\dfrac{32}{39}\\3,\\\dfrac{4}{5}-\dfrac{4}{-18}\\=\dfrac{4}{5}+\dfrac{4}{18}\\=\dfrac{72}{90}+\dfrac{20}{90}\\=\dfrac{72+20}{90}\\=\dfrac{92}{90}\\=\dfrac{46}{45}\\4,\\\dfrac{7}{21}-\dfrac{9}{-36}\\=\dfrac{7}{21}+\dfrac{9}{36}\\=\dfrac{1}{3}+\dfrac{1}{4}\\=\dfrac{4}{12}+\dfrac{3}{12}\\=\dfrac{4+3}{12}\\=\dfrac{7}{12}\\5,\\\dfrac{-12}{18}-\dfrac{-21}{35}\\=\dfrac{-12}{18}+\dfrac{21}{35}\\=\dfrac{-2}{3}+\dfrac{3}{5}\\=\dfrac{-10}{15}+\dfrac{9}{15}\\=\dfrac{\left(-10\right)+9}{15}\\=\dfrac{-1}{15}\\6,\\\dfrac{-3}{21}-\dfrac{6}{42}\\=\dfrac{-1}{7}-\dfrac{1}{7}\\=\dfrac{\left(-1\right)-1}{7}\\=\dfrac{-2}{7}\\7,\\\dfrac{-18}{24}-\dfrac{15}{21}\\=\dfrac{-3}{4}-\dfrac{5}{7}\\=\dfrac{-21}{28}-\dfrac{20}{28}\\=\dfrac{\left(-21\right)-20}{28}\\=\dfrac{-41}{28}\\8,\\=\dfrac{1}{6}-\dfrac{2}{5}\\=\dfrac{5}{30}-\dfrac{12}{30}\\=\dfrac{5-12}{30}\\=\dfrac{-7}{30}\\9,\\\dfrac{3}{5}-\dfrac{-7}{4}\\=\dfrac{3}{5}+\dfrac{7}{4}\\=\dfrac{12}{20}+\dfrac{35}{20}\\=\dfrac{12+35}{20}\\=\dfrac{47}{20}\\10,\\\left(-2\right)-\dfrac{-5}{8}\\=\left(-2\right)+\dfrac{5}{8}\\=\dfrac{-2}{1}+\dfrac{5}{8}\\=\dfrac{-16}{8}+\dfrac{5}{8}\\=\dfrac{\left(-16\right)+5}{8}\\=\dfrac{-11}{8}\\11,\\\dfrac{1}{-8}-\dfrac{-5}{9}\\=\dfrac{-1}{8}+\dfrac{5}{9}\\=\dfrac{-9}{72}+\dfrac{40}{72}\\=\dfrac{\left(-9\right)+40}{72}\\=\dfrac{31}{72}\\12,\\\dfrac{4}{13}-\dfrac{-\left(-12\right)}{39}\\=\dfrac{4}{13}-\dfrac{12}{39}\\=\dfrac{12}{39}-\dfrac{12}{39}\\=\dfrac{12-12}{39}\\=\dfrac{0}{39}\\=0.\end{array}\]