19.
\(a,=2x^3y^2+6xy^3-10xy^2\\ b,=8x^3-2x^2-4x^2+x-4x+1=8x^3-6x^2-3x+1\\ c,=-3x^2y^2+6x^2-9x\\ d,=\dfrac{1}{2}x^3+x^2-\dfrac{1}{2}x^2y-xy+\dfrac{3}{2}x+3\\ 20,\\ a,=2x\left(x^2-4x+4\right)=2x\left(x-2\right)^2\\ b,=2x\left(y+1\right)+z\left(y+1\right)=\left(2x+z\right)\left(y+1\right)\\ c,=\left(x+1\right)^2-y^2=\left(x-y+1\right)\left(x+y+1\right)\)
