Question

What is the sum of the arithmetic sequence 137, 125, 113 …, if there are 38 terms?

Answer 1

Sum `=-3230`

Explanation:

Given first term `a_1=137`
common difference `=-12`

number of terms `n=38`

compute the 38th term
`a_38=a_1+(n-1)*d`

`a_38=137+(38-1)*(-12)`

`a_38=-307`

Compute sum `S_38`

`S_38=n/2*(a_1+a_38)`

`S_38=38/2*(137+(-307))`

`S_38=-3230`

God bless...I hope the explanation is useful.