Question 1123342
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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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The r-th term is the difference between the first r terms and the sum of the first (n-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.


<U>Answer</U>.  10r - 7.  Options b).
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