a,x:2=\(\frac{x}{2}\)\(y:5=\frac{y}{5}\)
Áp dụng t/c:
\(\frac{x}{2}=\frac{y}{5}=\frac{x+y}{2+5}=\frac{21}{7}=3\)
\(\hept{\begin{cases}x=2.3\\y=5.3\end{cases}}\hept{\begin{cases}x=6\\y=15\end{cases}}\)
Vậy x=6;y=15
b,\(\frac{2a+3b-c}{\left(2.3\right)+\left(8.3\right)-5}=\frac{50}{25}=2 \)
\(=\hept{\begin{cases}a=3.2\\b=8.2\\c=5.2\end{cases}}=\hept{\begin{cases}a=6\\b=16\\c=10\end{cases}}\)
Vậy a=6;b=16;c=10