Giải thích các bước giải:
a/ `x^2(5x^3-x-\frac{1}{2})`
$=x^2.5x^3-x^2.x-x^2.\dfrac{1}{2}$
$=5x^5-x^3-\dfrac{1}{2}x^2$
b/ $(3xy-x^2+y).\dfrac{2}{3}x^2y$
$=3xy.\dfrac{2}{3}x^2y-x^2.\dfrac{2}{3}x^2y+y.\dfrac{2}{3}x^2y$
$=2x^3y^2-\dfrac{2}{3}x^4y+\dfrac{2}{3}x^2y^2$
c/ `(4x^3-5xy+2x)(-\frac{1}{2}xy)`
$=-\dfrac{1}{2}xy.4x^3+\dfrac{1}{2}xy.5xy-\dfrac{1}{2}xy.2x$
$=-2x^4y+\dfrac{5}{2}x^2y^2-x^2y$
Chúc bạn học tốt !!!