1+2+3+.......9999

49995000

2006-10-29 19:04:13 補充：
怎麼會想問這種問題呢?我算了許久答案不知有錯嗎?

1+2+3+...+9999
=(1+9999)x9999/2
=10000x9999/2
=99990000/2
=49995000

1+2+3+.......9999=49995000

(1+n)n/2
=(1 + 9999)9999/2
= 49995000

(1+9999)*9999/2
=10000*9999/2
=5000*9999
=49995000

there is a equation for this
n x (n+1)/2

9999 x (10000)/2

= 49995000

(1+9999)x9999÷2=49995000

9999/2 再X(1+9999)=49995000

(1+9999)x9999
----------------------
2

=49995000

(1+9999)9999/2
=49995000