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The 6th term of a G.P is -2 and its first term is 18. What…

The 6th term of a G.P is -2 and its first term is 18. What is the common ratio?
  • A.
    –1/2
  • B.
    -1/3
  • C.
    1/4
  • D.
    2
  • E.
    3
Correct Answer: Option B
Explanation

a, ar, ar2, ar3, ar4, ar5
6th term = ar5 = 2/27
1st term = a = 18
=> ar5 = 18r5 = 2/27

r5 =

-2/18 x 27

=

-1/9 x 27
r5 =

-1/243
√r5 = 5√-1/243

= -1/3

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