Bài 1:
a) \(\dfrac{x}{4}=\dfrac{y}{7}=\dfrac{x+y}{4+7}=\dfrac{55}{11}=5\)
\(\Rightarrow\left\{{}\begin{matrix}x=5.4=20\\y=5.7=35\end{matrix}\right.\)
b) \(\dfrac{x}{23}=\dfrac{y}{15}=\dfrac{2y}{30}=\dfrac{x-2y}{23-30}=\dfrac{14}{-7}=-2\)
\(\Rightarrow\left\{{}\begin{matrix}x=\left(-2\right).23=-46\\y=\left(-2\right).15=-30\end{matrix}\right.\)
Bài 2:
a) \(\dfrac{x}{15}=\dfrac{y}{12}=\dfrac{z}{7}=\dfrac{x-y+z}{15-12+7}=\dfrac{30}{10}=3\)
\(\Rightarrow\left\{{}\begin{matrix}x=3.15=45\\y=3.12=36\\z=3.7=21\end{matrix}\right.\)
b) \(\dfrac{x}{2}=\dfrac{y}{3}=\dfrac{z}{4}=\dfrac{x+y-z}{2+3-4}=\dfrac{-5}{1}=-5\)
\(\Rightarrow\left\{{}\begin{matrix}x=\left(-5\right).2=-10\\y=\left(-5\right).3=-15\\z=\left(-5\right).4=-20\end{matrix}\right.\)
