\(\frac{2x}{42}-\frac{28}{3x}=0\Leftrightarrow\frac{x}{21}-\frac{28}{3x}=0\Leftrightarrow\frac{x^2}{21x}-\frac{196}{21x}=0\Leftrightarrow\left(x-14\right)\left(x+14\right)=0\Leftrightarrow\hept{\begin{cases}x-14=0\\x+14=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=14\\x=-14\end{cases}}}\)