SELECT * FROM question_mgmt as q WHERE id=1009 AND status=1 SELECT id,question_no,question,chapter FROM question_mgmt as q WHERE courseId=2 AND subId=6 AND chapterId=80 and ex_no='2' AND status=1 ORDER BY CAST(question_no AS UNSIGNED) CBSE Free NCERT Solution of 11th mathematics Sequence and Series if the sum of nbsp n nbsp terms of an a p is 3n2

Question:

If the sum of n terms of an A.P. is 3n2 + 5n and its mth term is 164, find the value of m.

Answer:

Let a and b be the first term and the common difference of the A.P. respectively.

am = a + (m – 1)d = 164 … (1)

Sum of n terms,S subscript n space space end subscript equals space n over 2 open square brackets 2 a plus left parenthesis n minus 1 right parenthesis d close square brackets

Here,

n over 2 open square brackets 2 a plus n d minus d close square brackets equals 3 n squared plus 5 n rightwards double arrow n a space plus space n squared. d over 2 equals 3 n squared plus 5 n

Comparing the coefficient of n2 on both sides, we obtain

d over 2 equals 3 rightwards double arrow d equals 6

Comparing the coefficient of n on both sides, we obtain

a minus d over 2 equals 5 rightwards double arrow a minus 3 equals 5 rightwards double arrow a equals 8

Therefore, from (1), we obtain

8 + (m – 1) 6 = 164

⇒ (m – 1) 6 = 164 – 8 = 156

⇒ m – 1 = 26

⇒ m = 27

Thus, the value of m is 27.


< Previous Question

Next Question >

SELECT ex_no,question,question_no,id,chapter FROM question_mgmt as q WHERE courseId='2' AND subId='6' AND ex_no!=0 AND status=1 and id!=1009 ORDER BY views desc, last_viewed_on desc limit 0,10

  • Popular questions of class 11 Mathematics

SELECT ex_no,question,question_no,id,chapter FROM question_mgmt as q WHERE courseId='2' AND subId='6' AND ex_no!=0 AND status=1 and id!=1009 ORDER BY last_viewed_on desc limit 0,10

  • Recently Viewed Questions of Class 11 Mathematics

Comments

  • Answered by Ekta Mehta
  • 4 months ago

Taking Screenshots on your Samsung Galaxy M31s is very easy and quick.

  • Answered by Ekta Mehta
  • 4 months ago

Taking Screenshots on your Samsung Galaxy M31s is very easy and quick.

  • Answered by Ekta Mehta
  • 4 months ago

Taking Screenshots on your Samsung Galaxy M31s is very easy and quick.

Comment(s) on this Question


NCERT Solutions

Quick Links

Resources

Support