(7-x)(3-x)(2-x)(2+x)-100 =-[(x-7)(x+2)(x-3)(x-2)+100]=-[(x^2-5x-14)(x^2-5x+6)+100]=-[(x^2-5x-4-10)(x^2-5x-4+10)+100]=-[(x^2-5x-4)^2-100+100]=-(x^2-5x-4)^2 (初中就分解到这)