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anonymous

  • one year ago

Find the sum of a finite geometric sequence from n = 1 to n = 6, using the expression -2(5)n - 1. 1,223 -1,023 7,812 -7,812

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  1. anonymous
    • one year ago
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    @dan815

  2. welshfella
    • one year ago
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    Sn = a1 * r^n - 1 -------- r - 1

  3. welshfella
    • one year ago
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    here a1 = -2 , r = 5, n = 6

  4. anonymous
    • one year ago
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    Sn = -2 * 5^6 - 1 = 15624 -------- ------- = -7812.5 5 - 1 4

  5. anonymous
    • one year ago
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    Is that right?

  6. welshfella
    • one year ago
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    -7812

  7. anonymous
    • one year ago
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    Can you help me with this one: Find the sum of a finite arithmetic sequence from n = 1 to n = 15, using the expression 2n + 5.

  8. welshfella
    • one year ago
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    i'm assuming 2n + 5 is the formula for the nth term so first term would be 2+ 5 = 7 and 15th term would be 2(15) + 5 = 35 Sn = (n/2) ( a + l) here n = number of terms, a = first term and l = last ( 15th) term

  9. anonymous
    • one year ago
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    I dont understand what to do

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