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Homework Statement
Find the sum of the series 1-3+5-7+-11+...+1001
Homework Equations
I have no idea on this one....
I do know that the sum formula is Sn=n(t1+tn)/2
That formula only applies to arithmetic sequences and this is not an arithmetic sequence.
The first thing you will need to do is clarify the sum: 1-3+5-7+-11+...+1001. the first numbers, in absolute value, 1, 3, 5, and 7 differ by 2 but then there is the jump to 11, 4 larger than 7. Is it supposed to be 1-3+5-7+9-11+...+1001? If so then you can rewrite it 1+ (5-3)+ (9-7)+ (13- 11)+ ...+ (1001-999)= 1+ 2+ 2+ 2+ ...+ 2. Now, how many "2"s are there? How many pairs of odd numbers are there from 5 to 1001?