Question

in an ap Sn = 3n^2/2 +13n/2 find 25 term

Answer 1

 sum = 3n²/2 + 13n/2

as we know that nth term = (Sum of nth term ) -( sum of (n-1)th term

so 25th term = (sum of 25 terms) - ( sum of 24 terms)

                    =(3×(25)²/2 +(13×25)/2) - ( 3×(24)²/2 + (13×24)/2)

                    = 1100 - 1020

hence,                     = 80