a, Áp dụng t/c dtsbn:
\(\dfrac{x}{3}=\dfrac{y}{8}=\dfrac{z}{1}=\dfrac{x+y-z}{10}=\dfrac{x+y+z}{12}\\ \Rightarrow\dfrac{x+y-z}{x+y+z}=\dfrac{10}{12}=\dfrac{5}{6}\)
b, \(7y=4z\Rightarrow\dfrac{y}{z}=\dfrac{4}{7}\)
\(\Rightarrow\dfrac{y}{z}=\dfrac{x+y}{t+z}\Rightarrow yt+yz=xz+yz\\ \Rightarrow yt=xz\\ \Rightarrow\dfrac{x}{t}=\dfrac{y}{z}=\dfrac{4}{7}\)
c, \(\dfrac{3x-y}{x+y}=\dfrac{3}{4}\Rightarrow12x-4y=3x+3y\Rightarrow9x=7y\)
\(\Rightarrow\dfrac{x}{y}=\dfrac{7}{9}\)
d, Áp dụng t/c dtsbn:
\(\dfrac{a}{b}=\dfrac{b}{c}=\dfrac{c}{a}=\dfrac{a+b+c}{a+b+c}=1\\ \Rightarrow\left\{{}\begin{matrix}b=a=2012\\c=a=2012\end{matrix}\right.\Rightarrow a=b=c=2012\)
