1/
a/ $\dfrac{x^2-x}{x+3}=0$
$\leftrightarrow x^2-x=0$
$\leftrightarrow x(x-1)=0$
\(\leftrightarrow\left[ \begin{array}{l}x=0\\x-1=0\end{array} \right.\) \(\leftrightarrow\left[ \begin{array}{l}x=0\\x=1\end{array} \right.\)
b/ $\dfrac{x^2-2x+2}{x^2-5x+6}=0$
$\leftrightarrow x^2-2x+2=0$
$\leftrightarrow (x^2-2x+1)+1=0$
$\leftrightarrow (x-1)^2=-1$
mà $(x-1)^2\ge 0$
$\to x\in \varnothing$
2/ $3a-b=5\to b=3a-5$
Thế $b=3a-5$ vào biểu thức $M$:
$M=\dfrac{5a-3a+5}{2a+5}-\dfrac{3(3a-5)-3a}{2(3a-5)-5}$
$=\dfrac{2a+5}{2a+5}-\dfrac{9a-15-3a}{6a-15}$
$=1-\dfrac{6a-15}{6a-15}=1-1=0$
