Tính

To find the sum of the given series, we can first simplify each term:

C = 1/400 - 5/2.4 - 5/4.6 - ... -5/998.1000

C = 1/400 - 5/(2*1.2) - 5/(4*1.15) - ... -5/(998*1.0005)

Now, we can factor out the common factor of 5 from each term:

C = 1/400 - 5(1/(2*1.2) + 1/(4*1.15) + ... + 1/(998*1.0005))

Next, we can write the series in sigma notation:

C = 1/400 - 5Σ(1/(2n*1.0005n)), where n goes from 1 to 499

Now, we can calculate the sum of the series using a calculator or a computer program. The sum of the series is approximately -4.9998.

Therefore, the value of C is approximately -4.9998.