Question

How do you find the sum of the series `k` from k=1 to 20?

Answer 1

`sum_(k=1)^20 k = 210`

Explanation:

We need the standard formula `sum_(r=1)^n r=1/2n(n+1)`

`:. sum_(k=1)^20 k = 1/2(20)(20+1)`
`:. sum_(k=1)^20 k = 1/2(20)(21)`
`:. sum_(k=1)^20 k = 210`