The series -1+2-3+4-5+6...-99+100 is an example of an arithmetic series.
To find the sum of an arithmetic series, we can use the formula:
S = (n/2)(a + l)
where S is the sum of the series, n is the number of terms, a is the first term, and l is the last term.
In this case, the first term is -1, the last term is 100, and there are 100 terms in the series.
Plugging these values into the formula, we get:
S = (100/2)(-1 + 100)
S = 50(-1 + 100)
S = 50(99)
S = 4950
Therefore, the sum of the series -1+2-3+4-5+6...-99+100 is 4950.