a: \(\Leftrightarrow x\cdot\dfrac{2}{5}=\dfrac{2}{5}-\dfrac{1}{4}=\dfrac{3}{20}\)
hay \(x=\dfrac{3}{20}:\dfrac{2}{5}=\dfrac{3}{8}\)
b: \(\Leftrightarrow35x+49-8+12x=28x+126+112\)
\(\Leftrightarrow37x-28x=238-41=197\)
hay x=197/9
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