Tính:
a) \(\dfrac{-1}{24}-\left[\dfrac{1}{4}-\left(\dfrac{1}{2}-\dfrac{7}{8}\right)\right]\)
b)\(\left(\dfrac{5}{7}-\dfrac{7}{5}\right)-\left[\dfrac{1}{2}-\left(-\dfrac{2}{7}-\dfrac{1}{10}\right)\right]\)
c) \(\left(-\dfrac{1}{2}\right)-\left(-\dfrac{3}{5}\right)+\left(-\dfrac{1}{9}\right)+\dfrac{1}{71}-\left(-\dfrac{2}{7}\right)+\dfrac{4}{35}-\dfrac{7}{18}\)
`(-1)/24 - [ 1/4 - ( 1/2 - 7/8) ]`
`=(-1)/24 - [ 1/4 - ( 4/8 - 7/8)]`
`=(-1)/24 -[1/4 - (-3)/8]`
`=(-1)/24 - [1/4 + 3/8]`
`= (-1)/24 - [ 2/8 + 3/8]`
`=(-1)/24 - 5/8`
`= (-2)/3`
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`(5/7 - 7/5) - [ 1/2 - ( -2/7 - 1/10)]`
` = (5/7 - 7/5) - [ 1/2 - (2/7 + 1/10)]`
`=(5/7 - 7/5) - [ 1/2- (-27)/70]`
`=(5/7 - 7/5) - [ 1/2 +27/70]`
` = (25/35 - 49/35) - [ 35/70 + 27/70]`
` = (-24)/35 - 62/70`
`=(-24)/35 - 31/35`
`= -11/7`
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`(-1)/2 - (-3)/5 + (-1)/9 + 1/71 - (-2)/7 + 4/35 - 7/18`
` = (-1)/2 + 3/5 -1/9 + 1/71 + 2/7 + 4/35 - 7/18`
` = (-1/2 -1/9 - 7/18) + (3/5 + 2/7 + 4/35) +1/71`
` = ( -9/18 - 2/18 - 7/18) + ( 21/35 + 10/35 +4/35) + 1/71`
` = (-18)/18 + 35/35 + 1/71`
` = -1 + 1 + 1/71`
` = 0 + 1/71`
` = 1/71`
\(-\dfrac{1}{24}-\left[\dfrac{1}{4}-\left(\dfrac{1}{2}-\dfrac{7}{8}\right)\right]\)
\(=-\dfrac{1}{24}-\left[\dfrac{1}{4}-\left(\dfrac{4}{8}-\dfrac{7}{8}\right)\right]\)
\(=-\dfrac{1}{24}-\left[\dfrac{1}{4}-\left(-\dfrac{3}{8}\right)\right]\)
\(=-\dfrac{1}{24}-\left(\dfrac{1}{4}+\dfrac{3}{8}\right)\)
\(=-\dfrac{1}{24}-\left(\dfrac{2}{8}+\dfrac{3}{8}\right)\)
\(=-\dfrac{1}{24}-\dfrac{5}{8}=-\dfrac{1}{24}-\dfrac{15}{24}=-\dfrac{16}{24}=-\dfrac{2}{3}\)