(x-1)(x-2)(x-3)(x-4)-48

=[(x^2-5x)+4][(x^2-5x)+6]-48

t=x^2-5x

t^2+10t+24-48

t^2+10t-24

(t+12)(t-2)

(x^2-5x+12)(x^2-5x-2)