Expand[(x-2)(3x-1)(x+2)]

f[x_]:=4-12 x-x^2+3x^3

Manipulate[
Plot[{f[x],a*f[x]},{x,-6,6},PlotRange->{-20,40}],
{{a,1},-3,3}]

Manipulate[
Plot[{f[x],f[a*x]},{x,-6,6},PlotRange->{-20,40}],
{{a,1},-3,3}]

Manipulate[
Plot[{f[x],f[a*x+b]},{x,-6,6},PlotRange->{-20,40}],
{{a,1},-3,3},{{b,0},-3,3}]

Manipulate[
Plot[{f[x],f[a*(x+b)]},{x,-6,6},PlotRange->{-20,40}],
{{a,1},-3,3},{{b,0},-3,3}]