a, Ta có:
\(2x=5y\Rightarrow\dfrac{x}{5}=\dfrac{y}{2}\)
Áp dụng tính chất dãy tỉ số bằng nhau , ta có:
\(\dfrac{x}{5}=\dfrac{y}{2}=\dfrac{3x-y}{15-2}=\dfrac{10}{13}\)
\(\Rightarrow x=\dfrac{10}{13}.5=\dfrac{50}{13}\)
\(y=\dfrac{10}{13}.2=\dfrac{20}{13}\)
b, Ta có:
\(\dfrac{x}{y}=\dfrac{3}{4}\Rightarrow4x=3y\)
\(\Leftrightarrow x=\dfrac{3y}{4}\)
Mà \(xy=108\)
\(\Leftrightarrow\dfrac{3y}{4}.y=108\)
\(\Leftrightarrow\dfrac{3}{4}y^2=108\)
\(\Leftrightarrow y^2=144\)
\(\Leftrightarrow\left[{}\begin{matrix}y=12\\y=-12\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}y=12\Rightarrow x=9\\y=-12\Rightarrow x=-9\end{matrix}\right.\)
