math help

(1+2+3+4+5+6+7+8......+999,998+999,999+1,000,000)/2
=[(1,000,001)(1,000,000)/2] /2
=(1,000,001)(1,000,000)/4
=1,000,001 * 250,000
=250000250000

2006-12-21 12:26:09 補充：
有條公式的1+2+3+4+.......n=(n+1)(n)/2eg:1+2+3+4+5=(5+1)(5)/2=30/2=15

(1+2+3+4+5+6+7+8......+999,998+999,999+1,000,000)/2=?
=(1+1,000,000)1000000/2/2=?
=1000001*1000000
= 1000001000000

應該係 2500025000

個數 順序話 就係 頭加尾/2 *1,000,000 唔知係唔係