Find the sum of 20 terms of the A.P. 1,4,7,10…..

Explanation

Let a be the first term and d be the common difference of the given A.P.

Then, we have `a=1` and `d=3`

we have to find sum of 20 terms of the given A.P.

Putting a=1,d=3,n=20 in
`S_n` = `n/2`​ `{2a+(n−1)d}, `we get

`S _20` = `20/2``{2×1+(20−1)×3}=10×59=590`