#### Answer

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

#### Work Step by Step

$$\eqalign{
& {a_1} = 4,{a_2} = 8,{a_3} = - 16,{a_4} = 32,{a_5} = 64,{a_6} = - 128,... \cr
& {\text{to verify that the sequence is geometric}}{\text{, divide each term except the first by }} \cr
& {\text{the preceding term}} \cr
& \frac{{{a_6}}}{{{a_5}}} = \frac{{ - 128}}{{64}} = - 2 \cr
& \frac{{{a_5}}}{{{a_4}}} = \frac{{64}}{{32}} = 2 \cr
& {\text{the ratio is not constant}}{\text{, so}} \cr
& {\text{the sequence is not geometric }} \cr} $$