Question 8
The sum of first n terms of an AP is given by Sn = 2n2 + 3n . Find the sixteenth term of the AP.
Given
Sn = 2n2 + 3n
Taking n = 1
S1 = 2 12 + 3 1
= 2 + 3
= 5
So, Sum of first term of AP is 5
But sum of first term will be the first term
So, First term = a = 5
Taking n = 2 in Sn
S1 = 2 22 + 3 2
S2 = 2 4 + 6
S2 = 8 + 6
S2 = 14
Sum of first 2 terms is 14
Finding 2nd term
Sum of first 2 terms is 14
First term + Second term = 14
5 + a2 = 14
a2 = 14 5
a2 = 9
Hence in AP ,
First term = a = 3
Common difference = d = Second term First term
= 9 5
= 4
We need to find 16th term
We know that
an = a + (n 1) d
a16 = a + (16 1) d
= a + 15d
= 5 + 15 4
= 5 + 60
= 65
Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.
Hi, it looks like you're using AdBlock :(
Displaying ads are our only source of revenue. To help Teachoo create more content, and view the ad-free version of Teachooo... please purchase Teachoo Black subscription.
Please login to view more pages. It's free :)
Teachoo gives you a better experience when you're logged in. Please login :)
Solve all your doubts with Teachoo Black!
Teachoo answers all your questions if you are a Black user!