Đáp án:
b. \(\left\{ \begin{array}{l}
x = 20\\
y = 12\\
z = 42
\end{array} \right.\)
c. \(\left\{ \begin{array}{l}
y = 36\\
x = 27\\
z = 60
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
b.\left\{ \begin{array}{l}
\frac{x}{{10}} = \frac{y}{6}\\
\frac{x}{{10}} = \frac{z}{{21}}\\
5x + y - 2z = 28
\end{array} \right.\\
\to \left\{ \begin{array}{l}
y = \frac{3}{5}x\\
z = \frac{{21}}{{10}}x\\
5x + \frac{3}{5}x - \frac{{21}}{5}x = 28
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 20\\
y = 12\\
z = 42
\end{array} \right.\\
c.\left\{ \begin{array}{l}
x = \frac{3}{4}y\\
z = \frac{5}{3}y\\
2.\frac{3}{4}y - 3y + \frac{5}{3}y = 6
\end{array} \right.\\
\to \left\{ \begin{array}{l}
y = 36\\
x = 27\\
z = 60
\end{array} \right.
\end{array}\)
