a)\(x^3-2y^3-3xy^2\)
\(=x^3+2x^2y+xy^2-2y^3-4xy^2-2x^2y\)
\(=x\left(x^2+2xy+y^2\right)-2y\left(x^2+2xy+y^2\right)\)
\(=\left(x-2y\right)\left(x^2+2xy+y^2\right)\)
\(=\left(x-2y\right)\left(x+y\right)^2\)
b)\(x^6-x^4-2x^3+2x^2\)
\(=x^2\left(x^4-x^2+2x+2\right)\)
\(=x^2\left(x^2-2x+1\right)\left(x^2+2x+2\right)\)
\(=x^2\left(x-1\right)^2\left(x^2+2x+2\right)\)