a
\(\left(\dfrac{2x}{7}+1\right).4=-\dfrac{1}{28}\Leftrightarrow\dfrac{2x.}{7}+1=-\dfrac{1}{4.28}\)
\(\Leftrightarrow\dfrac{2x}{7}=-1-\dfrac{1}{28}\Leftrightarrow\dfrac{2x}{7}=\dfrac{-4.28-1}{4.4.7}\)
\(\Leftrightarrow2x=\dfrac{-\left(4.28+1\right)}{4.4}\)
\(\Leftrightarrow x=\dfrac{-\left(4.25+4.3+1\right)}{4.4.2}=\dfrac{-113}{2^5}=-\dfrac{113}{32}\)
b
\(2x-\left(x-3\right)=\dfrac{1}{2}\Leftrightarrow2x-x+3=\dfrac{1}{2}\)
\(x=\dfrac{1}{2}-3=\dfrac{1-2.3}{2}=\dfrac{-5}{2}\)
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