Find an explicit rule for the nth term of the sequence. 7, 21, 63, 189, ... select one: a. an = 7 • 3n b. an = 7 • 3n - 1 c. an = 3 • 7n - 1 d. an = 7 • 3n 1

If you look at by making a guess.

a = 7*3ⁿ, n = 0, 1, 2, 3, ...

Test:

when n = 0, a = 7*3⁰ = 7 * 1 = 7

when n = 1, a = 7*3¹ = 7 * 3 = 21

when n = 2, a = 7*3² = 7 * 9 = 63

when n = 3, a = 7*3³ = 7 * 27 = 189

So a = 7*3ⁿ, n = 0, 1, 2, 3, ...