Thực hiện phép tính (a) (2xy^3−4y−8x)(−1/2y). (b) (3x^4y^3−9x^2y^2+15xy^3):xy^2.

a) \(\left( {2x{y^3} - 4y - 8x} \right)\left( { - \;\frac{1}{2}y} \right) = - x{y^4} + 2y2 + 4xy.\)

b) \(\left( {3{x^4}{y^3} - 9{x^2}{y^2} + 15x{y^3}} \right):x{y^2} = 3{x^3}y - 9x + 15y\)

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

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