Cho xyz = 1. Tính giá trị biểu thức A = x/ x +x+1 + y / yz+y+1 + z/ xz +z+1

\(A = \frac{x}{{xy + x + 1}} + \frac{y}{{yz + y + 1}} + \frac{z}{{xz + z + 1}}\)

\[A = \frac{{xz}}{{xyz + xz + z}} + \frac{{xyz}}{{xz\left( {yz + y + 1} \right)}} + \frac{z}{{xz + z + 1}}\]

\[A = \frac{{xz}}{{xyz + xz + z}} + \frac{1}{{xy{z^2} + xyz + xz}} + \frac{z}{{xz + z + 1}}\]

\[A = \frac{{xz}}{{1 + xz + z}} + \frac{1}{{z + 1 + xz}} + \frac{z}{{xz + z + 1}}\]

\[A = \frac{{xz + z + 1}}{{xz + z + 1}}\]

A = 1.