Which choice is the explicit formula for the following geometric sequence

-0.1, 0.03, -0.009, 0.0027, -0.00081, ...

A. an = 0.1(0.3)n
B. an = 0.3(-0.3)n-1
C. an = -0.1(0.3)n-1
D. an = -0.1(-0.3)n-1
E. an = 0.1(-0.3)n-1

0.03 ÷ -0.1 = -0.3

D

I think you mean -0.1(-0.3)^(n - 1)

Dear Surf,

-0.1,0.03,-0.009,0.0027,-0.0008

This is a geometric sequence since there is a common ratio between each term. In this case, multiplying the previous term in the sequence by -0.3 gives the next term. In other words, an=r*an-1.
Geometric Sequence: r=-0.3

This is the form of a geometric sequence.
an=a1r^(n-1)

Substitute in the values of a1=-0.1 and r=-0.3.
an=-0.1*0.3^(n-1)
that is C a neg .1 and a pos .3

Even Wolfram states a_n = (-0.1)^n 3.^(n-1.) (for all terms given)
http://www.wolframalpha.com/input/?i=-0.…

Wh am I, see my videos in youtube type "kc9byk" or go to this link...
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Which choice is the explicit formula for the following geometric sequence?
-0.1, 0.03, -0.009, 0.0027, -0.00081, ...

D. an = -0.1(-0.3)n-1

D. an = -0.1(-0.3)n-1
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Ideas: a(1) = -0.1, r = -0.3

D. -0.1(-0.3)^(n-1)

Giving only the answer. The answer is (D.)