Question

Determine the number of terms n :

a 1 = 15, a n = 79, S n = 423

Answer 1

The number of terms in the sequence is 9

Explanation:

We want to get the number of terms

Mathematically, we have the formula for the sum of terms in an arithmetic sequence as

`sn = (n)/(2) (a + 1)`

a represents the first terms, and i represent the last term

`423 = (n)/(2) (15 + 79) \\ \\ 423 * 2 = 94(n) \\ \\ 94n = 846 \\ \\ n = (846)/(94) \\ \\ n = 9`