\(\frac{x+y}{x}+\frac{x+z}{y}+\frac{x+y}{z}+3\)
\(=\left(\frac{x+y}{z}+1\right)+\left(\frac{x+z}{y}+1\right)+\left(\frac{x+y}{z}+1\right)\)
\(=\frac{x+y+z}{z}+\frac{x+y+z}{y}+\frac{x+y+x}{z}\)
\(=\frac{0}{z}+\frac{0}{y}+\frac{0}{z}\)
\(=0\)
\(đk:x,y,z\ne0\)
\(\frac{y+z}{x}+\frac{x+z}{y}+\frac{x+y}{z}\)
\(=\left(\frac{y+z}{x}+1\right)+\left(\frac{x+z}{y}+1\right)+\left(\frac{x+y}{z}+1\right)-3+3\)
\(=\left(x+y+z\right)\left(\frac{1}{x}+\frac{1}{y}+\frac{1}{z}\right)=0\left(đpcm\right)\)