`11`
\(\dfrac{x+7}{x-7}-\dfrac{7}{x^2-7x}=\dfrac{1}{x}\left(ĐKXĐ:x\ne7,x\ne0\right)\\ \dfrac{x\left(x+7\right)}{x\left(x-7\right)}-\dfrac{7}{x\left(x-7\right)}=\dfrac{x-7}{x\left(x-7\right)}\\ x^2+7x-7=x-7\\ x^2+6x=0\\ x\left(x+6\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=0\\x+6=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\left(\text{loại}\right)\\x=-6\left(T/m\right)\end{matrix}\right.\)
`12`
\(\dfrac{x+5}{x}-\dfrac{x-7}{x+4}=\dfrac{x^2+35}{x^2+4x}\left(ĐKXĐ:x\ne0;x\ne-4\right)\\ \dfrac{\left(x+5\right)\left(x+4\right)}{x\left(x+4\right)}-\dfrac{x\left(x-7\right)}{x\left(x+4\right)}=\dfrac{x^2+35}{x\left(x+4\right)}\\ x^2+9x+20-x^2+7x=x^2+35\\ 16x-x^2-15=0\\ -\left(x^2-16x+15\right)=0\\ x^2-15x-x+15=0\\ x\left(x-15\right)-\left(x-15\right)=0\\ \left(x-15\right)\left(x-1\right)=0\\ \Rightarrow\left[{}\begin{matrix}x-15=0\\x-1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=15\left(T/m\right)\\x=1\left(T/m\right)\end{matrix}\right.\)
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