Big Ideas Math - Algebra 1, A Common Core Curriculum

Published by Big Ideas Learning LLC
ISBN 10: 978-1-60840-838-2
ISBN 13: 978-1-60840-838-2

Chapter 6 - Exponential Functions and Sequences - 6.6 - Geometric Sequences - Exercises - Page 336: 32

Answer

The equation for the $n$th term is $a_n=224(\frac{1}{2})^{n-1}$ and $a_6=7$

Work Step by Step

Write down the series from the graph. $224,112,56,28,...$ First term $a_1=224$. Common ratio $r=\frac{112}{224}=\frac{1}{2}$. Equation for a geometric sequence is $\Rightarrow a_n=a_1r^{n-1}$ Substitute $224$ for $a_1$ and $\frac{1}{2}$ for $r$. $\Rightarrow a_n=224(\frac{1}{2})^{n-1}$ Substitute $6$ for $n$. $\Rightarrow a_6=224(\frac{1}{2})^{6-1}$ Simplify. $\Rightarrow a_6=224(\frac{1}{2})^{5}$ $\Rightarrow a_6=7$.
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