To find the sum of the given sequence, we can group the terms in pairs:

((-2)+(-4)) + ((6)+8) + ((-10)+(-12)) + ... + ((-98)+(-100))

Simplifying each pair, we get:

-6 + 14 + -22 + ... + -198

Now, we can see that each pair has a difference of 8. So, we can rewrite the sequence as:

-6 + (-6+8) + (-6+8+8) + ... + (-6+8+8+...+8)

The last term in the sequence is -198, which can be written as (-6 + 8 + 8 + ... + 8).

Now, we can see that the sequence is just a repetition of (-6 + 8) for a total of 25 times. So, we can simplify the sequence as:

(-6 + 8) * 25

= 2 * 25

= 50

Therefore, the sum of the given sequence is 50.