LIVE Course for free

Rated by 1 million+ students
Get app now
0 votes
15 views
in Mathematics by (54.0k points)
closed by
If the sum of n terms of an AP  is 3n2 + 5n and its mth term is 164. Find the value of m ?
1. 160
2. 27
3. 29
4. 56

1 Answer

0 votes
by (30.0k points)
selected by
 
Best answer
Correct Answer - Option 2 : 27

Concept 

General term of an AP is given by:

an = Sn - S(n - 1)

Calculation:

Here Sn = 3n2 + 5n 

an = Sn - S(n - 1) 

After solving above equation we get 

an = 6n + 2 

For 1st term, put n = 1

So, a1 = 1 = 6 × 1 + 2 = 8

For 2nd term, put n = 2

So, a2 = 14

Now, common difference = d = a2 - a1 = 14 - 8 = 6

Given am = 164 

⇒ a + (m - 1)d = 164

⇒  8 + (m - 1 ) 6 = 164

∴ m = 27

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.

Categories

...