Ta co : \(\frac{x}{y}=\frac{7}{20};\frac{y}{z}=\frac{5}{8}\) va 2x+5y-2z=-15
\(\frac{x}{y}=\frac{7}{20}\Rightarrow\frac{x}{7}=\frac{y}{20};\frac{y}{z}=\frac{5}{8}\Rightarrow\frac{y}{5}=\frac{z}{8}\)
\(\frac{x}{7}=\frac{y}{20};\frac{y}{5}=\frac{z}{8}\Rightarrow\frac{x}{7}=\frac{5y}{20};\frac{20y}{20}=\frac{z}{8}\Rightarrow\frac{x}{35}=\frac{y}{20}=\frac{z}{160}\Rightarrow\frac{2x}{70}=\frac{5y}{100}=\frac{2z}{320}\)
Áp dụng tính chất dãy tỉ số bằng nhau , ta có :
\(\frac{2x}{70}=\frac{5y}{100}=\frac{2z}{320}=\frac{2x+5y-2z}{70+100-320}=-\frac{15}{-150}=0,1\)
Suy ra : \(\frac{2x}{70}=0,1\Rightarrow2x=0,1.70=7\Rightarrow x=7:2=3,5\)
\(\frac{5y}{100}=0,1\Rightarrow5y=100.0,1=10\Rightarrow y=10:5=2\)
\(\frac{2z}{320}=0,1\Rightarrow z=0,1.320=32\Rightarrow z=32:2=16\)
