SOLUTION: How do you find the two possible fourth values of a geometric sequence. There are two geometric sequences with 3rd term 5 and 5th term 80. What are the possible 4th terms?
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Question 1091273: How do you find the two possible fourth values of a geometric sequence. There are two geometric sequences with 3rd term 5 and 5th term 80. What are the possible 4th terms? Answer by ikleyn(52788) (Show Source):
= = 5 for the 3-rd term.
= = 80 for the 5-th term.
Take the ratio
= = 16 = = .
Thus you have an equation for "r": = 16, which has TWO solutions: r = 4 and/or r = -4.
So, the two possibilities for the 4-th term are
1) = = 5*4 = 20, and
2) = = 5*(-4) = -20.
