Bài 1 trang 17

Đề bài

Bỏ ngoặc rồi tính

a)\(\left( {\dfrac{{ - 3}}{8}} \right) + \left( {\dfrac{7}{9} - \dfrac{5}{8}} \right)\)

b)\(\dfrac{4}{9} - \left( {\dfrac{3}{7} + \dfrac{2}{9}} \right)\)

c)\(\left[ {\left( {\dfrac{{ - 2}}{5}} \right) + \dfrac{1}{3}} \right] - \left( {\dfrac{3}{5} - \dfrac{1}{4}} \right)\)

d)\(\left( {1\dfrac{1}{2} - \dfrac{3}{4}} \right) - \left( {0,25 + \dfrac{1}{2}} \right)\) 

Lời giải chi tiết

a) \(\left( {\dfrac{{ - 3}}{8}} \right) + \left( {\dfrac{7}{9} - \dfrac{5}{8}} \right)\)\( = \left( {\dfrac{{ - 3}}{8}} \right) - \dfrac{5}{8} + \dfrac{7}{9} =  - 1 + \dfrac{7}{9} = \dfrac{{ - 9}}{9} + \dfrac{7}{9} = \dfrac{{ - 2}}{9}\)

b) \(\dfrac{4}{9} - \left( {\dfrac{3}{7} + \dfrac{2}{9}} \right)\)=\(\dfrac{4}{9} - \dfrac{3}{7} - \dfrac{2}{9} = \dfrac{4}{9} - \dfrac{2}{9} - \dfrac{3}{7} = \dfrac{2}{9} - \dfrac{3}{7} = \dfrac{{14}}{{63}} - \dfrac{{27}}{{63}} = \dfrac{{ - 13}}{{63}}\)

c)\(\left[ {\left( {\dfrac{{ - 2}}{5}} \right) + \dfrac{1}{3}} \right] - \left( {\dfrac{3}{5} - \dfrac{1}{4}} \right)\)

 \(\begin{array}{l} = \left( {\dfrac{{ - 2}}{5}} \right) + \dfrac{1}{3} - \dfrac{3}{5} + \dfrac{1}{4}\\ = \left( {\dfrac{{ - 2}}{5}} \right) - \dfrac{3}{5} + \dfrac{1}{4} + \dfrac{1}{3}\\ = \left( { - 1} \right) + \dfrac{1}{4} + \dfrac{1}{3}\\ = \left( {\dfrac{{ - 12}}{{12}}} \right) + \dfrac{3}{{12}} + \dfrac{4}{{12}}\\ = \dfrac{{ - 5}}{{12}}\end{array}\)

d)\(\left( {1\dfrac{1}{2} - \dfrac{3}{4}} \right) - \left( {0,25 + \dfrac{1}{2}} \right)\)=\(\left( {\dfrac{3}{2} - \dfrac{3}{4}} \right) - \left( {\dfrac{1}{4} + \dfrac{1}{2}} \right) = \left( {\dfrac{3}{2} - \dfrac{1}{2}} \right) - \left( {\dfrac{3}{4} + \dfrac{1}{4}} \right) = 1 - 1 = 0\)