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anonymous

  • one year ago

find a_18 when a_1=27, d=-6

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  1. Jhannybean
    • one year ago
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    Using an arithmetic sequence that follows the formula: \(a_n =a_1 +(n-1)d\)

  2. anonymous
    • one year ago
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    -75 is my answer

  3. Jhannybean
    • one year ago
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    \[\large a_{\color{red}{n}} = a_{\color{red}{18}}\] Therefore we can conclude \(n=18\). Let's see..

  4. Jhannybean
    • one year ago
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    That is correct :)

  5. anonymous
    • one year ago
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    thank you, but i did it the long way, d=-6 a_1=27 a_n=?

  6. Jhannybean
    • one year ago
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    Perhaps you can show me how you've solved it?

  7. anonymous
    • one year ago
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    i did 27-6=21 21-6=15 15-6=9 and so on until i got to a18.

  8. anonymous
    • one year ago
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    but what is a_n?

  9. Jhannybean
    • one year ago
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    That's also a good way to go about finding it.

  10. anonymous
    • one year ago
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    it cant be 27(18-1)-6.

  11. Jhannybean
    • one year ago
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    And why do you think it cant be?

  12. anonymous
    • one year ago
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    because i got 453

  13. anonymous
    • one year ago
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    and -2754 if i do the negative sign, first answer (453) i did a minus sign

  14. Jhannybean
    • one year ago
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    This is how I solved it.\[a_n = a_{18} \longrightarrow n=18\]\[a_n=27+(18-1)(-6)\]\[a_n=27 -102\]\[a_n=-75\]

  15. anonymous
    • one year ago
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    thats why, i forgot the addition sign.

  16. Jhannybean
    • one year ago
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    :)

  17. anonymous
    • one year ago
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    thank you ma'am!

  18. Jhannybean
    • one year ago
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    No problem and good luck!

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