Đáp án:$a,5{x^5} - {x^3} - \dfrac{{{x^2}}}{2}\\$
$b,2{x^3}{y^2} - \dfrac{2}{3} \times {x^4}y + \dfrac{2}{3}{x^2}{y^2}\\$
$c,- 2{x^4}y + \dfrac{5}{2}{x^2}{y^2} - {x^2}y$
Giải thích các bước giải:
$a,{x^2} \times (5{x^3} - x - \dfrac{1}{2})\\
= {x^2} \times 5{x^3} - {x^2} \times x - {x^2} \times \dfrac{1}{2}\\
= 5{x^5} - {x^3} - \dfrac{{{x^2}}}{2}\\
b,(3xy - {x^2} + y) \times \dfrac{2}{3}{x^2}y\\
= 3xy \times \dfrac{2}{3}{x^2}y - {x^2} \times \dfrac{2}{3}{x^2}y + y \times \dfrac{2}{3}{x^2}y\\
= 2{x^3}{y^2} - \dfrac{2}{3} \times {x^4}y + \dfrac{2}{3}{x^2}{y^2}\\
c,(4{x^3} - 5xy + 2x) \times ( - \dfrac{1}{2}xy)\\
= 4{x^3} \times ( - \dfrac{1}{2}xy) - 5xy \times ( - \dfrac{1}{2}xy) + 2x \times ( - \dfrac{1}{2}xy)\\
= - 2{x^4}y + \dfrac{5}{2}{x^2}{y^2} - {x^2}y$
