Đáp án:
\(a)\,x:1\dfrac{2}{7}=-3,5\\\Rightarrow x:\dfrac{9}{2}=-\dfrac{7}{2}\\\Rightarrow x=-\dfrac{7}{2}.\dfrac{9}{2}\\\Rightarrow x=\dfrac{63}{4}\\b)\,0,4.x-\dfrac{1}{5}.x=\dfrac{3}{4}\\\Rightarrow x{\left(\dfrac{2}{5}-\dfrac{1}{5}\right)}=\dfrac{3}{4}\\\Rightarrow \dfrac{1}{5}x=\dfrac{3}{4}\\\Rightarrow x=\dfrac{3}{4}:\dfrac{1}{5}\\\Rightarrow x=\dfrac{15}{4}\)
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