a) Ta có: \(\left(x-2y\right)\left(x^2y^2-xy+2y\right)\)
\(=x^3y^2-x^2y+2xy-2x^2y^3+2xy^2-4y^2\)
b) Ta có: \(\left(x-y\right)\left(x^2+xy+y^2\right)\)
\(=x^3-y^3\)
c) Ta có: \(\left(\frac{1}{2}xy-1\right)\left(x^3-2x-6\right)\)
\(=\frac{1}{2}x^4y-x^2y-3xy-x^3+2x+6\)