Question

Find the sum of the first 40 terms of the arithmetic series: -5, -4, -3, -2, -1, … 580 600 620 640

Answer 1

I don't think it's possible, because the terms are not changing by the same amount each time.  At first they change by 1, then they change by 20.  With arithmetic series they need to have a COMMON DIFFERENCE.  If it's not common then it won't work.