Question

How do you find `S_n` for the arithmetic series given `a_1=5`, d=1/2, n=13?

Answer 1

`S_"13"=104]`

Explanation:

`S_"n" =n/2[(2a+(n-1)d]`

`S_"13"=13/2[(2(5)+(13-1)(1/2)]`
`S_"13"=13/2[10+(12)(1/2)]`
`S_"13"=13/2[10+6]`
`S_"13"=13/2[16]`
`S_"13"=104]`