Bài 1:
Cách 1:
\(A = \left( {3 + {1 \over 2} - {2 \over 3}} \right) - \left( {2 - {2 \over 3} + {5 \over 2}} \right) \)\(\;- \left( {5 - {5 \over 2} + {4 \over 3}} \right)\)
\(\eqalign{\;\;& = 3 + {1 \over 2} - {2 \over 3} - 2 + {2 \over 3} - {5 \over 2} - 5 + {5 \over 2} - {4 \over 3} \cr & = \left( {3 - 2 + 5} \right) + {1 \over 2} - {4 \over 3} \cr&= - 4 + {1 \over 2} - {4 \over 3} \cr & = {{ - 24 + 3 - 8} \over 6} = {{ - 29} \over 6}. \cr} \)
Cách 2:
\(A = \left( {{{18 + 3 - 4} \over 6}} \right) - \left( {{{12 - 4 + 15} \over 6}} \right) \)\(\,- \left( {{{30 - 15 + 8} \over 6}} \right)\)\(\; = {{17 - 23 - 23} \over 6} = {{ - 29} \over 6}.\)
Bài 2:
a) \(2x - 3 = x + {1 \over 2} \)
\(\Rightarrow 2x - x = {1 \over 2} + 3 \)
\(\Rightarrow x = {{1 + 6} \over 2}\)
\(\Rightarrow x = {7 \over 2}\)
b) \({{11} \over {12}} - \left( {{2 \over 5} + x} \right) = {2 \over 3}\)
\(\Rightarrow {{11} \over {12}} - {2 \over 5} - x = {2 \over 3}\)
\(\Rightarrow - x = {2 \over 3} - {{11} \over {12}} + {2 \over 5}\)
\( \Rightarrow - x = {{40 - 55 + 24} \over {60}}\)
\(\Rightarrow - x = {9 \over {60}} \)
\(\Rightarrow x = {{ - 9} \over {60}} = {{ - 3} \over {20}}.\)
