This is the basic and conceptual question from Chapter name- Arithmetic Progression
Chapter number- 9
Exercise 9.6
In this question we have been given that The sum of the first n terms of an A.P. is 4n2 + 2n.
Now we have to find the nth term of this A.P
CBSE DHANPAT RAI publications
Class:- 10th
Solutions of CBSE Mathematics
Question 40
Given Sn = 4n2 + 2n,
On putting n = 1, we get the first term(a), S1 = a = 4(1)2 + 2(1) = 6
On putting n = 2 gives S2 = a + a + d = 4(2)2 + 2(2) = 20
=> d = 20 – 2a
=> d = 20–12 = 8
By using the formula of nth term of an A.P.
an = a + (n – 1)d
So,
= 6 + (n – 1)8
= 6 + 8n – 8
= 8n – 2
Hence, the nth term of the given A.P. is 8n – 2.