Question

Calculate s26 for the arithmetic sequence in which a14=4.1 and the common difference is d=1.7

Answer 1

The value of
`s_(26)=84.5`

Explanation:

We have given
`a_(14)=4.1`

d=1.7

We have to find
`s_(26)`

So,
`a_(14)=a+13d` from the formula

`a_n=a+(n-1)d`

When n=14

`a_(14)=a+(14-1)(1.7)=a+13(1.7)`

`4.1=a+22.1`

`-18=a`

`a=-18`

Using the formula:

`s_n=(n)/(2)[2a+(n-1)d`

When n=26

`s_(26)=(26)/(2)[2(-18)+(26-1)(1.7)]`

On simplification we get:

`s_(26)=84.5`