Đáp án:
$\begin{array}{l}
a){\left( {3 - y} \right)^3}\\
= {3^3} - {3.3^2}.y + 3.3.{y^2} - {y^3}\\
= 27 - 27y + 9{y^2} - {y^3}\\
b){\left( {3x + 2{y^2}} \right)^3}\\
= 27{x^3} + 3.9{x^2}.2{y^2} + 3.3x.4{y^4} + 8{y^6}\\
= 27{x^3} + 54{x^2}{y^2} + 36x{y^4} + 8{y^6}\\
c){\left( {x - 3{y^2}} \right)^3}\\
= {x^3} - 3.{x^2}.3{y^2} - 3.x.9{y^4} - 27{y^6}\\
= {x^3} - 9{x^2}{y^2} - 27x{y^4} - 27{y^6}\\
d){\left( {\dfrac{x}{2} - y} \right)^3}\\
= \dfrac{{{x^3}}}{8} - 3.\dfrac{{{x^2}}}{4}y + 3.\dfrac{x}{2}.{y^2} - {y^3}\\
= \dfrac{{{x^3}}}{8} - \dfrac{3}{4}{x^2}y + \dfrac{3}{2}x{y^2} - {y^3}\\
e){\left( {\dfrac{x}{2} + \dfrac{y}{3}} \right)^3} = \dfrac{{{x^3}}}{8} + \dfrac{{{x^2}y}}{4} + \dfrac{{x{y^2}}}{6} + \dfrac{{{y^3}}}{{27}}\\
f){\left( {\dfrac{{2x}}{3} - 2y} \right)^3}\\
= \dfrac{{8{x^3}}}{{27}} - \dfrac{{4{x^2}y}}{3} + 8x{y^2} - 8{y^3}\\
g){\left( {x + y} \right)^3} + {\left( {x - y} \right)^3}\\
= {x^3} + 3{x^2}y + 3x{y^2} + {y^3}\\
+ {x^3} - 3{x^2}y + 3x{y^2} - {y^3}\\
= 2{x^3} + 6x{y^2}
\end{array}$
