+91-8076753736[email protected]
logo
logo
-->

Arithmetic Progressions

Question
CBSEENMA10009725
Wired Faculty App

The sum of first n terms of an AP is 3n2 + 4n. Find the 25th term of this AP.

Solution

Sn =3n2 + 4nFirst term ( a1 ) = S1 = 3 ( 1 )2 + 4 ( 1 ) = 7S2 = a1 + a2 = 3 ( 2 )2 + 4 ( 2 ) = 20a2 = 20 - a1 = 20 - 7 = 13So, comman difference ( d ) = a2 - a1 =13 - 7 =6Now,  an = a + ( n- 1 )d∴ a25 = 7 + ( 25 - 1 ) x 6            = 7 + 24 x 6            = 7 + 144            = 151

Some More Questions From Arithmetic Progressions Chapter

Write first four terms of the AP, when the first term a and the common difference d are given as follows:
a – 10, d = 10

Write first four terms of the AP, when the first term a and the common difference d are given as follows:
a = –2, d = 0

Write first four terms of the AP, when the first term a and the common difference d are given as follows:
a = 4, d = – 3

Write first four terms of the AP, when the first term a and the common difference d are given as follows:

a = – 1.25, d = – 0.25

For the following APs, write the first term and the common difference
3, 1, – 1, – 3, . . .

For the following APs, write the first term and the common difference
– 5, – 1, 3, 7, . . .

For the following APs, write the first term and the common difference
0.6, 1.7, 2.8, 3.9, . . .

Mock Test Series

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation