Question

How can you tell if a series is geometric or not? ie -2,6,-18,54

Answer 1

if there is a common factor in between terms, the series is geometric.
if you are adding or subtracting something, it is arithmetic
so... -2,6,-18,54 is geometric because there is a common factor -3 between terms, whereas 1,10,19,28... is arithmetic because you are adding 9 to get to the next term.

Answer 2

thanks