Đáp án:
$\begin{array}{l}
Dkxd:x\# 4\\
{x^2} - 3x = 0\\
\Leftrightarrow x = 0/x = 3\\
+ Khi:x = 0 \Leftrightarrow M = \dfrac{{x - 5}}{{x - 4}} = \dfrac{5}{4}\\
+ Khi:x = 3 \Leftrightarrow M = \dfrac{{3 - 5}}{{3 - 4}} = 2\\
b)Dkxd:x\# 0;\# 5\\
N = \dfrac{{x + 5}}{{2x}} - \dfrac{{x - 6}}{{5 - x}} - \dfrac{{2{x^2} - 2x - 50}}{{2{x^2} - 10x}}\\
= \dfrac{{\left( {x + 5} \right)\left( {x - 5} \right) + \left( {x - 6} \right).2x - 2{x^2} + 2x + 50}}{{2x\left( {x - 5} \right)}}\\
= \dfrac{{{x^2} - 25 + 2{x^2} - 12x - 2{x^2} + 2x + 50}}{{2x\left( {x - 5} \right)}}\\
= \dfrac{{{x^2} - 10x + 25}}{{2x\left( {x - 5} \right)}}\\
= \dfrac{{{{\left( {x - 5} \right)}^2}}}{{2x\left( {x - 5} \right)}}\\
= \dfrac{{x - 5}}{{2x}}
\end{array}$
