Bài 1:
a) Ta có: \(0,\left( {26} \right) = 0,262626... > 0,261.\)
b) Ta có: \( - {1 \over 3} = - 0.3333... < - 0.333.\)
Bài 2: Ta có:
\(3.{1 \over 2}.{4 \over {49}} - \left[ {2,\left( 4 \right).2{5 \over {11}}} \right]\,:\,\left( { - {{42} \over 5}} \right)\)
\( = {7 \over 2}.{4 \over {49}} - {{22} \over 9}.{{27} \over {11}}\,:\,\left( { - {{42} \over 5}} \right) \)
\(= {2 \over 7} + 6.{5 \over {42}} = {2 \over 7} + {5 \over 7}\)
Bài 3:
\(\left| {4x - \sqrt 2 } \right| = 0,\left( 4 \right) \)
\(\Rightarrow \left| {4x - \sqrt 2 } \right| = {4 \over 9} \)
\(\Rightarrow 4x - \sqrt 2 = {4 \over 9}\) hoặc \(4x - \sqrt 2 = - {4 \over 9} \)
\(\Rightarrow x = {{\sqrt 2 } \over 4} + {1 \over 9}\) hoặc \(x = {{\sqrt 2 } \over 4} - {1 \over 9}.\)
