$*$ Cách 1:
`3(x-1)(x-2)-x(3x+1)(1-x)`
`=(3x-3)(x-2)-(3x^2+x)(1-x)`
`=3x(x-2)-3(x-2)-3x^2(1-x)-x(1-x)`
`=3x^2-6x-3x+6-3x^2+3x^3-x+x^2`
`=3x^3+(3x^2-3x^2+x^2)+(-6x-3x-x)+6`
`=3x^3+x^2-10x+6`
$*$ Cách 2:
`3(x-1)(x-2)-x(3x+1)(1-x)`
`=3[x(x-2)-(x-2)]-x[3x(1-x)+(1-x)]`
`=3(x^2-2x-x+2)-x(3x-3x^2+1-x)`
`=3(x^2-3x+2)-x(-3x^2+2x+1)`
`=3x^2-9x+6+3x^3-2x^2-x`
`=3x^3+(3x^2-2x^2)+(-9x-x)+6`
`=3x^3+x^2-10x+6`