Chapter 12 - Sequences and Series - 12.1 Geometric Sequences - 12.1 Exercises - Page 612: 20

$${\text{the sequence is not geometric }}$$

$$\eqalign{ & {a_1} = 6,{a_2} = 8,{a_3} = 10,{a_4} = 12,{a_5} = 14,... \cr & {\text{to verify that the sequence is geometric}}{\text{, divide each term except the first by }} \cr & {\text{the preceding term}} \cr & \frac{{{a_5}}}{{{a_4}}} = \frac{{14}}{{12}} = \frac{7}{6} \cr & \frac{{{a_4}}}{{{a_3}}} = \frac{{12}}{{10}} = \frac{6}{5} \cr & {\text{the ratio is not constant}}{\text{, so}} \cr & {\text{the sequence is not geometric }} \cr} $$