Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 12 - Section 12.3 - Geometric Sequences - 12.3 Exercises - Page 865: 47

Answer

The ninth term of the sequence equals 6.

Work Step by Step

The general equation for the nth term of a geometric sequence is $a_n = a(r)^{n-1}$ where a = the first term and r = the common ratio. Since r is given as $\frac{1}{2}$ and a is given as 1536 plug these into the equation to get $a_n = 1536(\frac{1}{2})^{n-1}$. To find which number term of the sequence = 6 set the equation equal to 6 and solve for n: 6 = $1536(\frac{1}{2})^{n-1}$ 1. To solve: Divide each side by 1536: .00390625 = $\frac{1}{2}^{n-1}$ 2. Take the log base .5 of each side to further isolate n: 8 = n-1 3. n =9 The 9th term of the sequence equals 6.
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