Question

Given a geometric sequence with a1=5 and a4=135 find a2.

Answer 1

Answer:

  15

Step-by-step explanation:

Terms in a geometric series that are n apart will have a ratio that is r^n. Here we have terms a4 and a1, which are 4-1=3 apart, so their ratio is ...

  a4/a1 = 135/5 = 27 = r^3

  r = ∛27 = 3

The second term is the first, multiplied by this common ratio:

  a2 = a1·r = 3(5)

  a2 = 15