Question

How do you find the sum of the arithmetic sequence given a1 = 5, an = 3, n = 20?

Answer 1

`=color(blue)(80`

Explanation:

The formula for sum of an A.P when the first term `a1`, number of terms `n` and last term `an` are given is:

`color(blue)(Sum = (n/2)(a1+an)`

`= 20 /2 (5+3)`

`= 10 xx 8`

`=color(blue)(80`