ridgeboy36
What is the sum of a 6-term geometric series if the first term is 8 and the last term is 134,456 ? Answers to choose from.
a)129,513
b)130,624
c)156,864
d)172,846
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cwrw238
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let the first term = a
then 6th term =ar^5
where r = common ration
can you find r from this information?
ridgeboy36
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i might need some guidance but let me try!
cwrw238
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ok
ridgeboy36
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i really dont know how i got this but i ended up with 832 as the common ratio.
cwrw238
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6tt term = 134456 = ar^5
ist term = 8
so ar^5/a = r^5 = 134456/8 = 16807
cwrw238
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|dw:1357256722836:dw|
cwrw238
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you can now find the sum of the 6 terms by plugging in the values of a and r into the formula
sum = a * r^n - 1
------
r - 1
ridgeboy36
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ohh i see what i di wrong !! i was way off
ridgeboy36
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im almost done
cwrw238
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the value of n (number of terms) is 6
ridgeboy36
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okayy i got c)156,864
cwrw238
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right , good job
ridgeboy36
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thankyou
cwrw238
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yw