Question 1011566
To find the sum of the first {{{n}}} terms of an arithmetic sequence use the formula,


{{{S[n]= n(a[1]+a[n])/2}}}


if {{{S[n]=(2n^2)-n}}}, we have


{{{(2n^2)-n= n(a[1]+a[n])/2}}}....solve for the general term {{{a[n]}}}


{{{2(2n^2-n)/n= a[1]+a[n]}}}


{{{2n(2n-1)/n= a[1]+a[n]}}}


{{{2(2n-1)= a[1]+a[n]}}}


{{{a[n]=2(2n-1)- a[1]}}}