SOLUTION: Using this formula sn=a1 (1-rN)÷1-r. Find the sum of 3+6+12+24...+192

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Question 841587: Using this formula sn=a1 (1-rN)÷1-r. Find the sum of 3+6+12+24...+192
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

Find the sum of 3+6+12+24...+192    |Geometric, r = 2

a%5Bn%5D+=+a%5B1%5D%2Ar%5E%28n-1%29

First Find 'n'

 +192+=+3%282%29%5E%28n-1%29

  64+=+%282%29%5E%28n-1%29    ⇒  (n-1) = 6, n = 7

S%5Bn%5D+=+a%5B1%5D%28%281-r%5En%29%2F%281-r%29%29

S%5B7%5D+=+3%28%281-%282%29%5E7%29%2F%28-1%29%29+=+381

Wish You the Best in your Studies.