Let f(x)=(x-1)x-2)(x-3)
Let's do the sign chart
color(white)(aaaaa)xcolor(white)(aaaaa)-oocolor(white)(aaaaa)1color(white)(aaaaa)2color(white)(aaaaa)3color(white)(aaaaa)+oo
color(white)(aaaaa)x-1color(white)(aaaaa)-color(white)(aaaaa)+color(white)(aaaa)+color(white)(aaa)+
color(white)(aaaaa)x-2color(white)(aaaaa)-color(white)(aaaaa)-color(white)(aaaa)+color(white)(aaa)+
color(white)(aaaaa)x-3color(white)(aaaaa)-color(white)(aaaaa)-color(white)(aaaa)-color(white)(aaa)+
color(white)(aaaaa)f(x)color(white)(aaaaaa)-color(white)(aaaaa)+color(white)(aaaa)-color(white)(aaa)+