Question

What is the 20th term of the arithmetic sequence 5, -1, -7, ?

Answer 1

`=a_20=color(blue)(-109`

Explanation:

The arithmetic sequence is
`5, -1, -7`

The common difference `d` of this sequence is
`d=-1-5 = -6`

The formula for `n_(th)` of an arithmetic series is:
`color(blue)(a_n = a+(n-1)(d)`

Here, `a = 5, d=-6, n=20`

So, `a_20 = 5 +19(-6`)

`=5-114`
`=color(blue)(-109`