Ответ:

  1. \(x-y+z=3+(-6)=-3\).
  2. \(3z-(x-y)=3\cdot(-6)-3=-18-3=-21\).
  3. \(x-2z-y=(x-y)-2z=3-2\cdot(-6)=3+12=15\).
  4. \(7(x-y)-3z=7\cdot3-3\cdot(-6)=21+18=39\).
  5. \(\frac{2}{x-y-z}=\frac{2}{3-(-6)}=\frac{2}{9}\).
  6. \(x-y-3z=3-3\cdot(-6)=3+18=21\).

Ответ: 1) −3; 2) −21; 3) 15; 4) 39; 5) \(\frac{2}{9}\); 6) 21.