Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 5 - Number Theory and the Real Number System - 5.7 Arithmetic and Geometric Sequences - Exercise Set 5.7 - Page 332: 150

Answer

The provided statement is falseand if the sequence is \[2,6,18,54,\ldots \]common ratio is same the given sequence will be G.P. It is known that the geometric sequence is; \[a,ar,a{{r}^{2}},a{{r}^{3}},a{{r}^{4}},\ldots \] Where a is first term and r is common ratio, \[\begin{align} & r=\frac{{{a}_{2}}}{{{a}_{1}}} \\ & =\frac{{{a}_{3}}}{{{a}_{2}}} \\ & =\frac{{{a}_{3}}}{{{a}_{4}}} \end{align}\]

Work Step by Step

In the provided sequence,\[{{a}_{1}}=2,{{a}_{2}}=6,{{a}_{3}}=24,{{a}_{4}}=120\], \[\begin{align} & {{r}_{1}}=\frac{6}{2} \\ & =3 \\ & {{r}_{2}}=\frac{24}{6} \\ & =4 \end{align}\] And, \[\begin{align} & {{r}_{3}}=\frac{120}{24} \\ & =5 \end{align}\] So, \[\begin{align} & {{r}_{1}}\ne {{r}_{2}} \\ & \ne {{r}_{3}} \end{align}\] Hence, the provided sequence is not geometric Sequence. If the sequence is \[2,6,18,54,\ldots \]common ratio is same the provided sequence will be G.P. Hence, the provided statement is false, if the sequence is \[2,6,18,54,\ldots \]common ratio is same the provided sequence will be G.P.
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