解 原式=(x-1)(x-7)(x-3)(x-5)-9
=(x^2-8x+7)(x^2-8x+15)
设x^2-8x+7=a 则
原式=a(a+8)-9
=a^2+8a-9
=(a-1)(a+9)
=(x^2-8x+6)(x^2-8x+16)