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Adam1994

  • 2 years ago

find the sum of the arithmetic sequence having the data given. a1 = 5, an = 3, n = 20

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  1. Chlorophyll
    • 2 years ago
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    Do you know which formula to apply?

  2. Adam1994
    • 2 years ago
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    I have no idea, I missed a few days of class and I came back to a whole new lesson. Kinda just tryin to get caught up right now

  3. Chlorophyll
    • 2 years ago
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    S_n = n ( a_1 + a_n ) / 2

  4. ngocthi0101
    • 2 years ago
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    chloro right

  5. Chlorophyll
    • 2 years ago
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    Do you know how to plug in?

  6. Adam1994
    • 2 years ago
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    nuh uh :/

  7. Chlorophyll
    • 2 years ago
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    Try a1 = ?

  8. ngocthi0101
    • 2 years ago
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    that easy

  9. ngocthi0101
    • 2 years ago
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    i can prove formula

  10. Chlorophyll
    • 2 years ago
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    Just go step by step!

  11. ngocthi0101
    • 2 years ago
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    no, sum sequense have formula, not step by step

  12. Chlorophyll
    • 2 years ago
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    @Adam1994 pls let me know a1?

  13. Adam1994
    • 2 years ago
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    a1=5

  14. Chlorophyll
    • 2 years ago
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    a_n?

  15. ngocthi0101
    • 2 years ago
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    ok, i know a litle english

  16. Adam1994
    • 2 years ago
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    a_n = 3

  17. Chlorophyll
    • 2 years ago
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    Would you double check this problem, I believe it's wrong!

  18. Chlorophyll
    • 2 years ago
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    Since n = 20 => we're looking for S_20

  19. Chlorophyll
    • 2 years ago
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    S_20 = 20 ( a_1 + a_20 ) / 2

  20. Chlorophyll
    • 2 years ago
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    Anyway, this is the formula for arithmetic Sum, just memorize it for your own benefit!

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