Life
Write each arithmetic series as the sum of terms, find each sum.
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Life
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|dw:1354171632278:dw|
Life
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is the answer 20?
RadEn
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it similar by :
3(1) + 3(2) + 3(3) + 3(4) + ... + 3(10)
= 3(1+2+3+4+...+10)
= ......
Life
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so im wrong, i thought you were supposed to use the formula, Sn=n(a1+an)/2
geoffb
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That wording is a bit interesting. Are there multiple questions like this to find the answer for, or just this one?
Life
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yea there are about 8 questions that are under that two part question
geoffb
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Your formula would work; you must have done it wrong.
geoffb
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\[S_{n} = \frac{n}{2} (a_{1} + a_{n})\]
Did you use 10 for \(n\) and 3 for \(a_{1}\)?
RadEn
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for : n=1 ----> 3(1) = 3
n=2 ----> 3(2) = 6
n=3 ----> 3(3) = 9
....
so on, the series be 3+6+9+....+30
yes, use the formula like @geoffb said :)
Life
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for n, i put 10, a1, i put 1, and for A n, i put 3
geoffb
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Okay, that's the problem.
\(a_{1}\) means the value of your first term (which is 3 times 1, or 3).
\(a_{n}\) means the value of your n-th term. In this case, n is 10, so the value of the 10th term is 3 times 10, or 30.
Life
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i got 75, am i right?
geoffb
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No. What is your calculation?
Life
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|dw:1354172733466:dw|
geoffb
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Why are you using 10 for \(a_{n}\)?
geoffb
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It wants \(a_{n}\), not \(n\).
Life
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|dw:1354173323720:dw|
geoffb
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That looks great.
Life
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ughhh finally!
Life
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so i get 330/2=165
geoffb
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Yup. :)