Given the initial expression,
[tex]3x(x^2-x-2)+2x(3-x)-7x[/tex]Simplify it as shown below
[tex]\begin{gathered} =3x*x^2-3x*x-3x*2+2x*3-2x*x-7x \\ =3x^3-3x^2-6x+6x-2x^2-7x \end{gathered}[/tex][tex]\begin{gathered} =3x^3-3x^2-2x^2-7x \\ =3x^3-5x^2-7x \end{gathered}[/tex]