(x-1)(x-2)(x-3)(x-4)-24 =[(x-1)(x-4)][(x-2)(x-3)]-24 =[(x^2-5x)+4][(x^2-5x)+6]-24 =(x^2-5x)^2+10(x^2-5x)+24-24 =(x^2-5x)^2+10(x^2-5x) =(x^2-5x)(x^2-5x+10) =x(x-5)(x^2-5x+10)