đk : x khác 0 ; 3
\(\Rightarrow x-5x+15=3x+7\Leftrightarrow-7x=-8\Leftrightarrow x=\dfrac{8}{7}\left(tm\right)\)
đk : x khác 0 ; 5
\(\Rightarrow\dfrac{x}{5-x}-\dfrac{3}{x}=\dfrac{4-x}{x-5}\Rightarrow-x^2-3\left(x-5\right)=x\left(4-x\right)\)
\(\Leftrightarrow-x^2-3x+15=4x-x^2\Leftrightarrow-7x=-15\Leftrightarrow x=\dfrac{15}{7}\left(tm\right)\)