maths

2009-12-21 1:15 am

1+2+3+......+999+1000+999+......+3+2+1=?

回答 (3)

2009-12-21 8:34 pm

✔ 最佳答案

using a formula (sorry i forget which formula)

1+2+3+......+999+1000+999+......+3+2+1
=1000x1000
=1000000

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2009-12-21 1:23 am

use formula (n/2)(a+l)
=(1000/2)(1+1000)+(999/2)(999+1)
=500500+499500
=1000000

參考: me

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2009-12-21 1:19 am

1+2+3+......+999
= (1 + 999) x 999 / 2
= 499500

1+2+3+......+999+1000+999+......+3+2+1
= (1+2+3+......+999) x 2 + 1000
= 1000000

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