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, …

B)  16, -8, 4, -2, 1

C) -15, -18, -21.6, -25.92, -31.104

E) 625, 125, 25, 5, 1

Explanation:

Part (A)

Divide each term over its previous term. If each result is the same, then we have a geometric sequence.

(term2)/(term1) = (-4)/(-2) = 2

(term3)/(term2) = (-6)/(-4) = 1.5

We can stop here since we got a different result.

This sequence is not geometric.

Part (B)

Same idea as part (A)

(term2)/(term1) = (-8)/16 = -0.5

(term3)/(term2) = 4/(-8) = -0.5

(term4)/(term3) = (-2)/4 = -0.5

(term5)/(term4) = 1/(-2) = -0.5

We get the same result each time. The common ratio is r = -1/2 = -0.5. This sequence is geometric.

Part (C)

(term2)/(term1) = (-18)/(-15) = 1.2

(term3)/(term2) = (-21.6)/(-18) = 1.2

(term4)/(term3) = (-25.92)/(-21.6) = 1.2

(term5)/(term4) = (-31.104)/(-25.92) = 1.2

This sequence is geometric since each result is the same. The common ratio is r = 1.2

note: 6/5 = 1.2

Part (D)

(term2)/(term1) = (10.5)/4 = 2.625

(term3)/(term2) = (17)/(10.5) = 1.619

We don't get the same result, so we can stop here. This sequence is not geometric.

Part (E)

(term2)/(term1) = (125)/(625) = 0.2

(term3)/(term2) = (25)/(125) = 0.2

(term4)/(term3) = (5)/(25) = 0.2

(term5)/(term4) = (1)/(5) = 0.2

The common ratio is r = 0.2 or r = 1/5

This sequence is geometric.

C) -15, -18, -21.6, -25.92, -31.104

E) 625, 125, 25, 5, 1

Step-by-step explanation:

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