SOLUTION: The 9th term and 6th term of geometric are 80 and 10.(a)find the 1st term and constant ratio.(b)find the number of terms if the last term is 5120.

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Question 1070726: The 9th term and 6th term of geometric are 80 and 10.(a)find the 1st term and constant ratio.(b)find the number of terms if the last term is 5120.
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
__, __, __, __, __, 80, __, __, 10

__, __, __, __, __, 80,80r,80r²,8r³=10
                                 r³=10/80
                                 r³=1/8
                                  r=1%2F2

a%5Bn%5D%22%22=%22%22a%5B1%5Dr%5E%28n-1%29

a%5B6%5D%22%22=%22%22a%5B1%5D%281%2F2%29%5E%286-1%29

80%22%22=%22%22a%5B1%5D%281%2F2%29%5E5

80%22%22=%22%22a%5B1%5D%281%2F32%29

2560%22%22=%22%22a%5B1%5D

Edwin