How do you know if the sequence $1, -2, -5, -8,...$ is arithmetic or geometric?

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Answer 1 · 2016-12-01T08:54:10

It is an arithmetic sequence

It is an arithmetic sequence because:

$a_n-a_(n-1)=-3 AAn$

that's

$-2-1=-5-(-2)=-8-(-5)...=-3$

How do you know if the sequence 1, -2, -5, -8,...1, -2, -5, -8,... is arithmetic or geometric?