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anonymous

  • one year ago

Identify whether the series summation of 12 open parentheses 3 over 5 close parentheses to the i minus 1 power from 1 to infinity is a convergent or divergent geometric series and find the sum, if possible.

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  1. anonymous
    • one year ago
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    \[\sum_{i=1}^{\infty} 12\frac{ 3}{ 5}^i-1\]

  2. anonymous
    • one year ago
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    It's suppose to be 12(3/5)^i-1

  3. anonymous
    • one year ago
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    This is a convergent geometric series. The sum cannot be found. This is a convergent geometric series. The sum is 30. This is a divergent geometric series. The sum cannot be found. This is a divergent geometric series. The sum is 30.

  4. anonymous
    • one year ago
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    I got A?

  5. phi
    • one year ago
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    \[ \sum_{i=1}^{\infty} 12\left(\frac{ 3}{ 5}\right)^{i-1} \]?

  6. anonymous
    • one year ago
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    yes:)

  7. phi
    • one year ago
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    I would change the i=1 to i=0 (and i-1 in the exponent to i) just so it looks "more standard" \[ \sum_{i=0}^{\infty} 12\left(\frac{ 3}{ 5}\right)^{i} \\ 12\sum_{i=0}^{\infty} \left(\frac{ 3}{ 5}\right)^{i} \] there is a standard formula for this

  8. anonymous
    • one year ago
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    no. It's (3/5)^i-1 not i=1

  9. phi
    • one year ago
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    ***no. It's (3/5)^i-1 not i=1*** yes, but I did this: let i= j+1 then i-1 becomes (j+1-1) = j and in the summation, the lower limit i=1 becomes j+1= 1 or j=0 and the upper limit stays infinity then I renamed j to i the summation part is \[ \frac{1-r^\infty}{1-r} \]

  10. anonymous
    • one year ago
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    Ohhh!!! Ok, I get it now! I realise that's what you were doing

  11. phi
    • one year ago
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    I did that so it looks like the "rule" \[ \sum_{i=0}^N r^i = \frac{1-r^N}{1-r} \]

  12. anonymous
    • one year ago
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    Yes, I agree

  13. phi
    • one year ago
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    r is 3/5 and we know r*r*r*... gets smaller and smaller, and if we do it enough times, it approaches zero. thus the summation is \[ \frac{1-0}{1-\frac{3}{5}} = \frac{1}{\frac{2}{5}}= \frac{5}{2}\] multiply by the leading 12, to get 12*5/2 = 30

  14. phi
    • one year ago
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    divergent means the sum "diverges" (fancy word for "moves away" ... from a fixed number) in other words, you don't get an answer if it diverges. cross off any answer with "diverges" because we found an answer.

  15. anonymous
    • one year ago
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    Ok, so we can cross offf C and D?

  16. anonymous
    • one year ago
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    Then the answer would be A? Right?

  17. phi
    • one year ago
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    choice A says there is no answer. But we can find the answer. (see up above)

  18. anonymous
    • one year ago
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    Sorry, I meant B :) Since we got 30 as an answer

  19. anonymous
    • one year ago
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    Thanks so much<3

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