n的阶乘怎么算？

Question

如题所述

Answer 1

解： 众所周知，n的阶乘是 n！=1×2×3×4×5× ..............（n-2）（n-1）n
=n(n-1)(n-2)(n-3)....................5×4×3×2×1
设 （x-1）=N, 则 N!=N(N-1)(N-2)(N-3)...................x5×4×3×2×1 即 （x-1）!=(x-1)(x-2)(x-3).....(x-6)(x-7).................×5 ×4×3×2×1
所以， (x-1)(x-2)(x-3).....(x-6)×(x-8)(x-9).....................(x-100)
=(x-1)!/(x-7)(x-101)(x-102)..............×5×4×3×2×1
=(x-1)!/(x-7)(x-101)!