Adam1994
find the sum of the arithmetic sequence having the data given.
a1 = 5, an = 3, n = 20



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Chlorophyll
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Do you know which formula to apply?

Adam1994
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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

Chlorophyll
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S_n = n ( a_1 + a_n ) / 2

ngocthi0101
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chloro right

Chlorophyll
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Do you know how to plug in?

Adam1994
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nuh uh :/

Chlorophyll
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Try a1 = ?

ngocthi0101
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that easy

ngocthi0101
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i can prove formula

Chlorophyll
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Just go step by step!

ngocthi0101
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no, sum sequense have formula, not step by step

Chlorophyll
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@Adam1994 pls let me know a1?

Adam1994
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a1=5

Chlorophyll
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a_n?

ngocthi0101
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ok, i know a litle english

Adam1994
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a_n = 3

Chlorophyll
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Would you double check this problem, I believe it's wrong!

Chlorophyll
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Since n = 20 => we're looking for S_20

Chlorophyll
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S_20 = 20 ( a_1 + a_20 ) / 2

Chlorophyll
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Anyway, this is the formula for arithmetic Sum, just memorize it for your own benefit!