SOLUTION: The sum of the first n terms of a series is 5n^2-2n. The r-th term is... a) 6r+3 b) 10r-7 c) 4r^2-r d) r(5r-2) e)3r

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Question 1123342: The sum of the first n terms of a series is 5n^2-2n. The r-th term is...
a) 6r+3 b) 10r-7 c) 4r^2-r d) r(5r-2) e)3r
Found 2 solutions by ikleyn, incline dybala:
Answer by ikleyn(52790)   (Show Source): You can put this solution on YOUR website!
.
The sum of the first n terms of a series is 5n^2-2n. The r’th term is...
a) 6r+3 b) 10r-7 c) 4r^2-r d) r(5r-2) e)3r
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 


The r-th term is the difference between the first r terms and the sum of the first (n-1) terms, i.e.


 = (5*r^2-2*r) - (5*(r-1)^2-2*(r-1)) = 


           = 5r^2 - 2r - 5r^2 + 10r - 5 + 2r - 2 = 10r - 7.


Answer.  10r - 7.  Options b).


Answer by incline dybala(1)   (Show Source): You can put this solution on YOUR website!
.

The r-th term is the difference between the first r terms and the sum of the first (r-1) terms, i.e.

a[r] = (5*r^2-2*r) - (5*(r-1)^2-2*(r-1)) =

= 5r^2 - 2r - 5r^2 + 10r - 5 + 2r - 2 = 10r - 7.

Answer. 10r - 7. Options b).

i got the answer from https://www.algebra.com/algebra/homework/word/misc/Miscellaneous_Word_Problems.faq.question.1123342.html



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