Answer :


Now, Sum of n terms



=


= n[5 + 2n–2]


=n[3 + 2n]


Now,



=


= (n + 1)[7 + n]




On cross multiplying we get,


16n[3 + 2n] = 17n + 17[7 + n]


48n + 32n2 = 119n + 17n2 + 119 + 17n


48n + 32n2 = 136n + 17n2 + 119


15n2 – 88n – 199 = 0


n =

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