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kiara23

  • 2 years ago

PLEASE HELP URGENT ! what is the 7th of the geometric sequence where a1 = 3 and a5 = -768

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  1. amistre64
    • 2 years ago
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    nothings THAT urgent :/

  2. amistre64
    • 2 years ago
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    we should start by remembering the general formula for a geometric sequence

  3. amistre64
    • 2 years ago
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    an = a1*r^(n-1)

  4. amistre64
    • 2 years ago
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    we know a1, and we know the value when n=5; from this we can grab the r value

  5. amistre64
    • 2 years ago
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    can you fill those in for me?

  6. kiara23
    • 2 years ago
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    kind of

  7. amistre64
    • 2 years ago
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    give it a try, ill know if its right or not :)

  8. kiara23
    • 2 years ago
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    the answer is going to be -3,072

  9. amistre64
    • 2 years ago
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    it might be, but lets see if we can build up to that

  10. kiara23
    • 2 years ago
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    ok

  11. amistre64
    • 2 years ago
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    lets fill in what we are given: a1 = 3 and a5 = -768 when n=5 an = a1 * r^(n-1) a5 = -786 = 3 * r^(5-1) -786/3 = r^(4) -292 = r^(4) , 4rt the whole thing to find r 4rt(-292) = r as is this is not a possible sequence to me. an even root can be negative across the reals

  12. amistre64
    • 2 years ago
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    an even root canNOT .... i passed typing class, honest :)

  13. amistre64
    • 2 years ago
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    check your problem and make sure you havent got an error in the post

  14. kiara23
    • 2 years ago
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    ok

  15. amistre64
    • 2 years ago
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    i got a feeling the a1 = -3 for this to work like you want it to

  16. kiara23
    • 2 years ago
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    yeah

  17. kiara23
    • 2 years ago
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    it is

  18. amistre64
    • 2 years ago
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    4rt(292) = r then this is what we get for r take the general formula again, knowing this r and n=7 a7 = -3 * (4rt(292))^(6) and a calculator should popout your intended results

  19. kiara23
    • 2 years ago
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    can it be 12,288

  20. amistre64
    • 2 years ago
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    no

  21. amistre64
    • 2 years ago
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    ...can what be?

  22. amistre64
    • 2 years ago
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    a7 is going to be a negative value

  23. kiara23
    • 2 years ago
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    -12,288

  24. amistre64
    • 2 years ago
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    adjust for a mismath and i get: a7 = -3 * 256^(6/4) = -12288 , so yes

  25. kiara23
    • 2 years ago
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    can you help me with thi one ? What is the sum of the geometric sequence -4, 28, -196 ?

  26. amistre64
    • 2 years ago
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    why did you think that the answer "is going to be -3,072"?

  27. kiara23
    • 2 years ago
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    i hd my ngatives wrng

  28. kiara23
    • 2 years ago
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    signs

  29. amistre64
    • 2 years ago
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    ah, itll prolly be best to post up a new question with that sum in it; i have to go for now

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