3 Answers:
B) 16, -8, 4, -2, 1
C) -15, -18, -21.6, -25.92, -31.104
E) 625, 125, 25, 5, 1
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Step-by-step 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.
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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.
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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
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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.
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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.