SOLUTION: If the 2nd and 5th term of a geometric progression are -6 48 respectively, find the sum of the 5th first four terms

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Question 1187380: If the 2nd and 5th term of a geometric progression are -6 48 respectively, find the sum of the 5th first four terms
Found 2 solutions by Boreal, ikleyn:
Answer by Boreal(15235) About Me  (Show Source):
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3 terms apart have a ratio of -8 in a geometric progression so r=-2. If second term is -6, first term is 3.
sum is a(1-r^n)/(1-r)
S= 3((1-(-2)^4)/(1-(-2))
=-45/3
=-15
the terms are 3, -6, 12, -24, 48
That is the first five terms, and the sum of the first four is -15

Answer by ikleyn(52787) About Me  (Show Source):
You can put this solution on YOUR website!
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    find the sum of the 5th first four terms.

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