數學:單數乘法

1 x 3 x 5 x 7 x 9 x...97 x 99
= 1 x 2 x 3 x ... x 99 x 100 / (2 x 4 x 6 x ... x 100)
= 1 x 2 x 3 x ... x 99 x 100 / (2^50)(1 x 2 x 3 x ... x 49 x 50)
= 100! / [(2^50)(50!)]




2010-05-13 19:14:52 補充：
= 2.725392138...... x 10^78

2010-05-13 19:19:11 補充：
2.725392138...小數點向後移78個位。

2010-05-14 21:44:57 補充：
個位數字 :

1 x 3 x 5 x 7 x 9 = 5尾

11 x 13 x 15 x 17 x 19 = 5尾

21 x 23 x 25 x 27 x 29 = 5尾

......

91 x 93 x 95 x 97 x 99 = 5尾

5尾 x 5尾 x ......x 5尾 = 5尾

個位數字 = 5

怎麼不停改暱稱呀???

1 x 3 x 5 x 7 x 9 x 11 x 13 ..... ............ x 97 x 99



= (1×2×3×...×100) / (2×4×6×...×100)



= 100! / [(2×1) × (2×2) × (2×3) × ... × (2×50)]



= 100! / [250 × (1×2×3×...×50)]
= 100! / [250 × 50!]