\(y=x+z\Rightarrow\hept{\begin{cases}x-y=-z\\y-z=x\end{cases}}\)
Ta ó: \(M=\left(1+\frac{x}{z}\right)\left(1-\frac{y}{x}\right)\left(1-\frac{z}{y}\right)\)
\(=\frac{x+z}{z}\cdot\frac{x-y}{y}\cdot\frac{y-z}{y}\)
\(=\frac{y}{z}\cdot\frac{-z}{x}\cdot\frac{x}{y}=-1\)
Vậy M=-1