1,2, - 3, - 4,5,6, - 7, - 8, () (number 2013)

1,2, - 3, - 4,5,6, - 7, - 8, () (number 2013)

This series of numbers takes 4 as the cycle, showing the positive, positive, negative and negative law
2013 △ 4 = more than 503 1
So: the number of 2013 is positive, that is, 2013

1 * 2 of 2013 + 2 * 3 of 2013 + 3 * 4 of 2013 + 4 * 5 of 2013 + 5 * 6 of 2013

1 * 2 of 2013 + 2 * 3 of 2013 + 3 * 4 of 2013 + 4 * 5 of 2013 + 5 * 6 of 2013
=2013x(1/1x2+1/2x3+1/3x4+1/4x5+1/5x6)
=2013x(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6)
=2013x(1-1/6)
=2013x5/6
=10065/6
If you don't understand this question, you can ask,

1+2-3-4+5+6-7-8+9+… +2010-2011-2012+2013

=(-1)×2012÷2+2013 =-1006+2013 =1007

2, negative 4, 6, negative 8, 10, negative 12, 1, negative 14, negative 16 According to the arrangement, what is the 99th number? What is the 100th number?
What method should be used for this kind of problem?

99 is 198
100 is - 200