Advertisements
Advertisements
Question
The sum of n terms of an A.P. is 3n2. The second term of this A.P. is ______.
Options
8
3
9
12
Advertisements
Solution
The sum of n terms of an A.P. is 3n2. The second term of this A.P. is 9.
Explanation:
Given Sn = 3n2;
Sn – 1 = 3(n – 1)2
∴ Tn = Sn – Sn–1
= 3n2 – 3(n – 1)2
= 3n2 – 3[n2 – 2n + 1] ...[∵ (a – b)2 = a2 – 2ab + b2]
= 3n2 – 3n2 + 6n – 3
= 6n – 3
∴ T2 = 6 × 2 – 3
= 12 – 3
= 9
APPEARS IN
RELATED QUESTIONS
Find the number of natural numbers between 101 and 999 which are divisible by both 2 and 5.
If Sn denotes the sum of first n terms of an A.P., prove that S30 = 3[S20 − S10]
Ramkali saved Rs 5 in the first week of a year and then increased her weekly saving by Rs 1.75. If in the nth week, her week, her weekly savings become Rs 20.75, find n.
Find the sum given below:
`7 + 10 1/2 + 14 + ... + 84`
Find the 8th term from the end of the AP 7, 10, 13, ..., 184.
The angles of a quadrilateral are in AP whose common difference is 10°. Find the angles.
Find the first term and common difference for the following A.P.:
5, 1, –3, –7, ...
Find the sum of all 2-digit natural numbers divisible by 4.
The sum of n terms of an A.P. is 3n2 + 5n, then 164 is its
Find the sum of first 17 terms of an AP whose 4th and 9th terms are –15 and –30 respectively.
