Question

HELP ! I've been stuck on this for over 15 mins. :(

What are the explicit equation and domain for an arithmetic sequence with a first term of 8 and a second term of 5?

an = 8 − 5(n − 1); all integers where n ≥ 1
an = 8 − 5(n − 1); all integers where n ≥ 0
an = 8 − 3(n − 1); all integers where n ≥ 1
an = 8 − 3(n − 1); all integers where n ≥ 0

Answer 1

a1 = first term = 8

Plug in a1 = 8:
an = 8 + (n - 1)d

FInd d:
Given that a2 = 5
5 = 8 + (2-1)d
5 = 8 + d
d = -3

Plug in d = -3:
an = 8 -3(n - 1)

Answer: an = 8 -3(n - 1) ; n ≥ 1