We have given a question from arithmetic progression chapter in which we have been asked to find the nth term and the 15th term of the AP, if the sum of the first n terms of an AP is (3n^2+6n).
Book – RS Aggarwal, Class 10, chapter 5C, question no 4
Rajan@2021Guru
The sum of the first n terms of an AP is (3n^2+6n). Find the nth term and the 15th term of this AP.
Share
We know, nth term Tn=a+(n−1)d
Where
a= First term
d= Common difference
n= number of terms
Tn=nth term
Given: Sn=3n2+6n
S1=3(1)2+6×1=3+6=9
S2=3(2)2+6×2=12+12=24
T2=S2−S1=24−9=15
d=15−9=6
a=9
Tn=a+(n−1)d=9+(n−1)×6
=9+6n−6=3+6n
=6n+3
T15=6×15+3
=90+3
=93.