The formula to find the sum of an arithmetic sequence is

`S_n=n/2(a_1+a_n)`

`S_50=50/2(1+50)`

`S_50=25(51)`

`S_50=1275`

The formula to find the sum of an arithmetic sequence is

`S_n=n/2(a_1+a_n)`

`S_50=50/2(1+50)`

`S_50=25(51)`

`S_50=1275`