\(\Rightarrow\left\{{}\begin{matrix}\dfrac{x}{7}=\dfrac{y}{20}\\\dfrac{y}{5}=\dfrac{z}{8}\end{matrix}\right.\)\(\Rightarrow\dfrac{x}{7}=\dfrac{y}{20}=\dfrac{z}{32}\)
Áp dụng t/c dtsbn:
\(\dfrac{x}{7}=\dfrac{y}{20}=\dfrac{z}{32}=\dfrac{2x}{14}=\dfrac{5y}{100}=\dfrac{2z}{64}=\dfrac{2x+5y-2z}{14+100-64}=\dfrac{-100}{50}=-2\)
\(\Rightarrow\left\{{}\begin{matrix}x=\left(-2\right).7=-14\\y=\left(-2\right).20=-40\\z=\left(-2\right).32=-64\end{matrix}\right.\)
63. vacation/ since/ we/ haven’t/ last/ had/ a/ year/ .
64. Ha Noi/ homeless/ give/ in/ clothes/ away/ they/ warm/ to/ people/ .
65. our/ a/ in/ makes/ volunteering/ difference/ community/.
66. health/ take/ good/ you/ should/ your/ because/ up/ is/ for/ jogging/ it/.
