Đáp án:
Áp dụng tính chất của dãy tỉ số bằng nhau ta có:
$\begin{array}{l}
a)x:y:z = 5:3:4\\
\Rightarrow \dfrac{x}{5} = \dfrac{y}{3} = \dfrac{z}{4} = \dfrac{{2y}}{6}\\
= \dfrac{{x + 2y - z}}{{5 + 6 - 4}} = \dfrac{{ - 121}}{7}\\
\Rightarrow \left\{ \begin{array}{l}
x = - \dfrac{{121}}{7}.5 = \dfrac{{ - 605}}{7}\\
y = - \dfrac{{121}}{7}.3 = \dfrac{{ - 363}}{7}\\
z = - \dfrac{{121}}{7}.4 = \dfrac{{ - 484}}{7}
\end{array} \right.\\
b)5x = 2y \Rightarrow y = \dfrac{5}{2}.x\\
3y = 5z \Rightarrow y = \dfrac{5}{3}.z\\
\Rightarrow \dfrac{5}{2}.x = y = \dfrac{5}{3}.z\\
\Rightarrow \dfrac{x}{{10}} = \dfrac{y}{5} = \dfrac{z}{{15}} = \dfrac{{x + y + z}}{{10 + 5 + 15}} = \dfrac{{ - 970}}{{30}} = \dfrac{{ - 97}}{3}\\
\Rightarrow \left\{ \begin{array}{l}
x = - \dfrac{{97}}{3}.10 = \dfrac{{ - 970}}{3}\\
y = - \dfrac{{97}}{3}.5 = \dfrac{{ - 485}}{3}\\
z = - \dfrac{{97}}{3}.15 = - \dfrac{{1455}}{3}
\end{array} \right.\\
c)\dfrac{x}{3} = \dfrac{y}{z}??
\end{array}$
Em kiểm tra lại đề bài ý c
