(X-1)(X-3)(X-5)(X-7)
=【(X-1)(X-7)】【(X-3)(X-5)】
=(x^2-8x+7)(x^2-8x+15)
楼主题目没说清楚,因此无法给出题目最终结果.估计楼主是说x^2-8x已知,代进去就可求解.