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anonymous

  • one year ago

What is the sum of the first 18 terms of the arithmetic series 11 + 15 + 19 + 23 + ⋯? a.) 684 b.) 810 c.) 831 d.) 846 Thank you!! <3 Your assistance will help me graduate! ^_^

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  1. anonymous
    • one year ago
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    \(\huge S_n=\dfrac{n(a_1+a_n)}{2}\) n is the last term of the sum, or in this case 18 a_1 is the first term in the series a_n is the 18th term

  2. anonymous
    • one year ago
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    and to find a_n we can use \(a_n=a_1+(n-1)d\) where d is the common difference so \(\large a_{18}=11+(18-1)d\)

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