a) \(\displaystyle ({x^2}y - 2{\rm{x}} - 2{\rm{z}})xy\).
Thay \(\displaystyle x =1; y = -1; z = 3\) ta có:
\(\displaystyle (1^2. (-1) – 2. 1 – 2. 3). 1 (-1) \)\(\displaystyle = (-1 – 2 – 6). (-1) = (-9). (-1) = 9\)
b) \(\displaystyle xyz + {{2{{\rm{x}}^2}y} \over {{y^2} + 1}}\).
Thay \(\displaystyle x = 1; y = -1; z = 3\) ta có:
\(\displaystyle 1.\left( { - 1} \right).3 + {{{{2.1}^2}.( - 1)} \over {{{( - 1)}^2} + 1}} \)\(\displaystyle = - 3 + {{ - 2} \over 2} = - 3 + ( - 1) = - 4\)
