SOLUTION: If an = 3n + 4, find the sum of the first 20 terms in the sequence.

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Question 1141644: If an = 3n + 4, find the sum of the first 20 terms in the sequence.
Answer by ikleyn(52787) About Me  (Show Source):
You can put this solution on YOUR website!
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It is arithmetic progression with the first term a%5B1%5D = 7, the common difference d = 3 and the number of terms n = 20.


Use the formula for the sum of the first "n" terms of an AP


    S%5Bn%5D = %28a%5B1%5D+%2B+%28%28n-1%29%2Ad%29%2F2%29%2An.


Substitute the given values into the formula


    S%5B20%5D = %287+%2B+%28%2820-1%29%2A3%29%2F2%29%2A20.


Now use your calculator (or computer) to get the numerical value.



Do not forget to post your "THANKS" to me when you complete this assignment.

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For introductory lessons on arithmetic progressions see
    - Arithmetic progressions
    - The proofs of the formulas for arithmetic progressions
    - Problems on arithmetic progressions
    - Word problems on arithmetic progressions
in this site.

Also,  you have this free of charge online textbook in ALGEBRA-II in this site
    - ALGEBRA-II - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this online textbook under the topic "Arithmetic progressions".


Save the link to this textbook together with its description

Free of charge online textbook in ALGEBRA-II
https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson

into your archive and use when it is needed.