Question

If the first two terms of a geometric sequence are 4 and 12, which of the following would be the 10th term?

A) 76
B) 84
C) 78,732
D) 236,196

Answer 1

78,732

Explanation:

a_1 = 4

a_2 = 12

a_2/a_1 = 12/4 = 3

a_1 = 4

a_2 = 4 * 3 = 4 * 3^1 = 12

a_3 = 4 * 3 * 3 = 4 * 3^2 = 36

a_n = 4 * 3^(n - 1)

For n = 10:

a_10 = 4 * 3^(10 - 1) = 4 * 3^9 = 4 * 19,683 = 78,732