Question

How do you find the sum of the arithmetic sequence given a1=3, d=-4, n=8?

Answer 1

`-88`

Explanation:

The sum to n terms of an arithmetic sequence is.

`color(orange)"Reminder"`

`color(red)(bar(ul(|color(white)(a/a)color(black)(S_n=n/2[2a+(n-1)d])color(white)(a/a)|)))`
where a is the first term, d the common difference and n, the terms being summed.

here a = 3 , d =- 4 and n = 8

`rArrS_8=8/2[(2xx3)+(7xx-4)]`

`=4(6-28)=-88`