Đáp án:
$\begin{array}{l}
a)\dfrac{6}{8} + \dfrac{{ - 19}}{{18}} + \dfrac{{ - 9}}{{12}}\\
= \dfrac{3}{4} + \dfrac{{ - 19}}{{18}} + \dfrac{{ - 3}}{4}\\
= \left( {\dfrac{3}{4} + \dfrac{{ - 3}}{4}} \right) + \dfrac{{ - 19}}{{18}}\\
= \dfrac{{ - 19}}{{18}}\\
b)\dfrac{{15.35 - 30}}{{45 + 19.15}}\\
= \dfrac{{15.35 - 15.2}}{{15.3 + 19.15}}\\
= \dfrac{{15.\left( {35 - 2} \right)}}{{15.\left( {3 + 19} \right)}}\\
= \dfrac{{33}}{{22}}\\
= \dfrac{{3.11}}{{2.11}}\\
= \dfrac{3}{2}\\
c)\dfrac{{3x}}{{46}} = \dfrac{{ - 6}}{{23}}\\
\Rightarrow \dfrac{{3.x}}{{46}} = \dfrac{{ - 12}}{{46}}\\
\Rightarrow 3.x = - 12\\
\Rightarrow x = - 4\\
Vậy\,x = - 4\\
d)\left( {2x + y} \right) \vdots \left( {x - 1} \right)\\
\Rightarrow 2x + y = k.\left( {x - 1} \right)\\
\Rightarrow y = k.x - k - 2x\\
\Rightarrow y = \left( {k - 2} \right).x - k\\
Vậy\,y = \left( {k - 2} \right).x - k\left( {k,x \in Z} \right)
\end{array}$
