Thực hiện phép tính (a) (3x^3−x^2y+2xy+3)−(3x^3−2x^2y−xy+3).

a) \(\left( {3{x^3} - {x^2}y + 2xy + 3} \right) - \left( {3{x^3} - 2{x^2}y - xy + 3} \right)\)

\[\begin{array}{l} = 3{x^3} - {x^2}y + 2xy + 3 - 3{x^3} + 2{x^2}y + xy - 3\\ = {x^2}y + 3xy\end{array}\]

b) \(\left( {x + 2y} \right)\left( {{x^2} + 3{y^2}} \right) = {x^3} + 3x{y^2} + 2{x^2}y + 6{y^3}\)

c) \(\left( {4{x^3}y{z^2} - 6x{y^3} + 9{x^2}{y^4}{z^3}} \right):2xy = 2{x^2}{z^2} - 3{y^2} + \frac{9}{2}x{y^3}{z^3}\)