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anonymous

  • one year ago

Find the sum of a finite arithmetic sequence from n = 1 to n = 15, using the expression 2n + 5. 315 215 32 35

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  1. anonymous
    • one year ago
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    @dan815

  2. anonymous
    • one year ago
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    @welshfella

  3. anonymous
    • one year ago
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    Please help! Ill give medals and become fan

  4. anonymous
    • one year ago
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    what is the first term, when \(n=1\)?

  5. anonymous
    • one year ago
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    I dont know

  6. anonymous
    • one year ago
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    really?

  7. anonymous
    • one year ago
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    replace \(n\) by \(1\) in \(2n+5\)

  8. anonymous
    • one year ago
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    so its 7?

  9. anonymous
    • one year ago
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    yes now hold that number

  10. anonymous
    • one year ago
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    what is \(2n+5\) if \(n=15\)?

  11. anonymous
    • one year ago
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    35?

  12. anonymous
    • one year ago
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    yes

  13. anonymous
    • one year ago
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    Is that the final answer?

  14. anonymous
    • one year ago
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    formula you are going to use is \[\frac{n}{2}(a_1+a_n)\] you have \(a_1=7,a_{15}=35\)

  15. anonymous
    • one year ago
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    what is\(7+35\)?

  16. anonymous
    • one year ago
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    Its 42

  17. anonymous
    • one year ago
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    ok so we are at \[\frac{15}{2}(42)\]

  18. anonymous
    • one year ago
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    divide 42 by 2, then multiply the result by 15

  19. anonymous
    • one year ago
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    Its 315

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