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Rainbow_Dash

  • 3 years ago

Find S_n for the given arithmetic series. a _1= 10, d = –9, n = 15

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  1. micahwood50
    • 3 years ago
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    And what does d represent?

  2. Rainbow_Dash
    • 3 years ago
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    common difference

  3. Callisto
    • 3 years ago
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    Formula to use: \[S_{n}=a_n + (n-1)d\]

  4. Rainbow_Dash
    • 3 years ago
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    is that first one a_1 or a_n

  5. Callisto
    • 3 years ago
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    I must be crazy somehow. Just a minute. Forget the previous post first!!

  6. Callisto
    • 3 years ago
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    Here it goes. \[S_{n} = \frac{n}{2} [2a + (n-1)d]\] a = first term, d=common difference , n=number of terms

  7. Rainbow_Dash
    • 3 years ago
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    okay thanks :)

  8. Rainbow_Dash
    • 3 years ago
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    do'nt ask why but the question changed, and now i just need to write an equation.

  9. Callisto
    • 3 years ago
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    Sorry for my silly mistakes :( I suppose the first one I wrote was for \(a_n\). but still, it's wrong! \(a_n=a_1+(n-1)d\)

  10. Rainbow_Dash
    • 3 years ago
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    thank you for your help :) this newest one is to find a_n, and once i have a_n i use the 2nd one you put?

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