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anonymous

  • one year ago

Find the sum of the arithmetic sequence. -10, -7, -4, -1, 2, 5, 8 11 -70 0 -7

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  1. anonymous
    • one year ago
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    @misssunshinexxoxo

  2. anonymous
    • one year ago
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    @peachpi

  3. anonymous
    • one year ago
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    Goshhh cant you add them just add them you get -7

  4. anonymous
    • one year ago
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    oh so all i do is add?

  5. anonymous
    • one year ago
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    that's what I'd do since they're listed

  6. anonymous
    • one year ago
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    what if they give me only 4 terms and tell me to find the sum of the first 9

  7. anonymous
    • one year ago
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    nevermind all you do is find the difference then find the first 9 terms then add them right?

  8. anonymous
    • one year ago
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    Find the sum of the first 9 terms of the sequence. Show all work for full credit. 2, -7, -16, -25, ...

  9. anonymous
    • one year ago
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    for that one they probably want to see you use the formulas. Can you come up with a equation for a_n using the formula?

  10. anonymous
    • one year ago
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    n-9?

  11. anonymous
    • one year ago
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    Well ye but if you should use equations same thing so d=+3 and they are 7 terms so n=7 S(7)=7/2 (-10+8)=7/2(2) =7

  12. anonymous
    • one year ago
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    this one. where you have to find d and a_1 \[a_n=a_1+d(n-1)\]

  13. anonymous
    • one year ago
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    Sorry -7*

  14. anonymous
    • one year ago
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    so an=2 + -9(n-1)?

  15. anonymous
    • one year ago
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    This is a straight arithmetic sequence guys no need for this d is simply d=Un+1 -Un

  16. anonymous
    • one year ago
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    yes. and they want the sum of the first 9 so now find a_9

  17. anonymous
    • one year ago
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    a9 would = -70 right?

  18. anonymous
    • one year ago
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    yes. Now for the sum use this formula \[S_n=\frac{ n }{ 2 }(a_1+a_n)\] so \[S_9=\frac{ n }{ 2 }(a_1+a_9)\]

  19. anonymous
    • one year ago
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    so the sum would =-306

  20. anonymous
    • one year ago
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    yes

  21. anonymous
    • one year ago
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    The sum of the first 9 is 18 S9=n/2 ( 2a1+(n-1)d = 9/2 (-20+24) =36/2 =18

  22. anonymous
    • one year ago
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    Oh sorry used another sequence

  23. anonymous
    • one year ago
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    @joyraheb different set of numbers from the sequence at the very top

  24. anonymous
    • one year ago
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    ok good because i was about to say, i thought i finally understood this then that messed me up hahaha

  25. anonymous
    • one year ago
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    but thank you!

  26. anonymous
    • one year ago
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    Oh ok so d=-9 so S9=-4.5(-14+90)= -342 right?

  27. anonymous
    • one year ago
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    no s9= (9/2)(2+(-70)) = -306

  28. anonymous
    • one year ago
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    because of this equation Sn=n/2(a1+an) @joyraheb

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