Question

Which sequences are geometric? Check all that apply.

–2, –4, –6, –8, –10, …
16, –8, 4, –2, 1
–15, –18, –21.6, –25.92, –31.104, …
4, 10.5, 17, 23.5, 30, …
625, 125, 25, 5, 1, …

Answer 1

geometric is when each term increased by the same ratio as the previous one

example
if there are terme, x,y,z in a seqence
the sequence is geometric if
y/x=z/y

so

first one
-4/2=-6/4, -2=-1.5, no

2nd
-8/16=4/-8, -1/2=-1/2, yes

3rd one
-18/-15=-21.6/-18, 1.2=1.2, yes

4th one
10.5/4=17/10.5, 2.625=1.619, no

5th one
125/625=25/125, 1/5=1/5, yes

the ones that are geometric are

16, –8, 4, –2, 1
–15, –18, –21.6, –25.92, –31.104, …
625, 125, 25, 5, 1, …