A geometric sequence is defined recursively by an = 4an-1. The 10th term of the sequence is a10 = 3.5. What is a13?

1 Answer
Alan P.
Jul 9, 2015

Using (I think) a different interpretation of the question than Spandy's answer (which I'm not certain I understand):
#color(white)("XXXX")##a_13 = 224#

Explanation:

Assuming the "givens" are:
#color(white)("XXXX")##a_n=4a_(n-1)#
#color(white)("XXXX")##a_10 = 3.5#

#a_11 = 4*a_10 = 4*3.5 = 14#

#a_12 = 4*a_11 = 4*14 = 56#

#a_13 = 4*a_12 = 4*56 = 224#

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