Question

the sum of first n term of an ap is 3n^2 +4n . find the 25 term of this ap

Answer 1

Simply substitute 25 in place of n in above formula u'll get the answer

Answer 2

first put n =1
3×1+4×1=7
now put n=2
3×4+4×2=20
as we know sn=n/2 (2a +(n-1)d)
s25=25/2(2(7)+(25-1)13)
=1975