\(\frac{x}{12}=\frac{y}{9}=\frac{z}{8}\) => \(\frac{x-y}{12-9}=\frac{15}{3}=5\)=> x = 60 ; y= 45 ; z=40 => x-y-z = 60-45-40 =-25
\(\frac{x}{2}=\frac{2y}{3}=\frac{3z}{4}\Leftrightarrow\frac{x}{2}=\frac{y}{\frac{3}{2}}=\frac{z}{\frac{4}{3}}\)
Áp dụng t/c dãy tỉ số=nhau:
\(\frac{x}{2}=\frac{y}{\frac{3}{2}}=\frac{z}{\frac{4}{3}}=\frac{x-y}{2-\frac{3}{2}}=\frac{15}{\frac{1}{2}}=30\)
=>x/2=30=>x=60
y/3/2=30=>y=30.3/2=45
z/4/3=30=>z=30.4/3=40
Vậy x-y-z=60-45-40=-25