\(\dfrac{-3x}{4}\left(\dfrac{3}{x}+\dfrac{5}{7}\right)\)\(=0\)
\(\Leftrightarrow\dfrac{-9x}{4x}+\dfrac{-15x}{28}=0\)
\(\Leftrightarrow\dfrac{-9}{4}+\dfrac{-15x}{28}=0\)
\(\Leftrightarrow\dfrac{-15x}{28}=\dfrac{9}{4}\)
\(\Leftrightarrow x=\dfrac{9}{4}:\dfrac{-15}{28}=\dfrac{9}{4}.\dfrac{-28}{15}=\dfrac{-252}{60}=\dfrac{-21}{5}\)
Bn T.I.C.K mk nhe!!^_^