Question

Làm tính nhân:

a)      \(\left( {xy} \right).\left( {{x^2} + xy - {y^2}} \right)\);

b)      \(\left( {xy + yz + zx} \right).\left( { - xyz} \right)\). 

Answer 1

a)

\(\begin{array}{l}\left( {xy} \right).\left( {{x^2} + xy - {y^2}} \right)\\ = xy.{x^2} + xy.xy - xy.{y^2}\\ = {x^3}y + {x^2}{y^2} - x{y^3}\end{array}\)

b)

\(\begin{array}{l}\left( {xy + yz + zx} \right).\left( { - xyz} \right)\\ = xy.\left( { - xyz} \right) + yz.\left( { - xyz} \right) + zx.\left( { - xyz} \right)\\ =  - {x^2}{y^2}z - x{y^2}{z^2} - {x^2}y{z^2}\end{array}\)