Fewpal
0 votes
16 views
in Arithmetic Progression by (25.5k points)

If the sum to first n terms of an A.P. is (3n2/2 + 5n/2), find its 25th term.

Please log in or register to answer this question.

1 Answer

0 votes
by (4.4k points)

⇒ S2 = 11

∴ a2 = S2 – S1 = 11 – 4 = 7

Taking n = 3, we get

⇒ S3 = 21

∴ a3 = S3 – S2 = 21 – 11 = 10

So, a = 4,

d = a2 – a1 = 7 – 4 = 3

Now, we have to find the 25th term

an = a + (n – 1)d

a25 = 4 + (25 – 1)3

a25 = 4 + 24 × 3

a25 = 4 + 72

a25 = 76

Hence, the 25th term is 76.

Welcome to Sarthaks eConnect: A unique platform where students can interact with teachers/experts/students to get solutions to their queries. Students (upto class 10+2) preparing for All Government Exams, CBSE Board Exam, ICSE Board Exam, State Board Exam, JEE (Mains+Advance) and NEET can ask questions from any subject and get quick answers by subject teachers/ experts/mentors/students.

...