3, - 6,9, - 12 , - 2004, 2007, 2010, complete the following questions: (1) write the 100th number in this column; (2) Find the sum of this column

3, - 6,9, - 12 , - 2004, 2007, 2010, complete the following questions: (1) write the 100th number in this column; (2) Find the sum of this column

(1).-3
(2) . 3, - 6,9, - 12... - 2004, 2007 are all multiples of 3,
And even digits are negative, so 100 digits are - 300
There are: 2007 / 3 = 669 items in this series
The sum of every two items is - 3, so the sum of this column is:
-3*(669-1)/2+2007=1005
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