Adv
deepaksoni
  • 0
Guru

Question 46. If the sum of first n terms of an A.P. is (3n^2 +7n)/2 then find its nth term. Hence, write its 20th term.

  • 0

This is the basic and conceptual question from Chapter name- Arithmetic Progression
Chapter number- 9
Exercise 9.6

In this question we have been given that the sum of first n terms of an A.P. is (3n^2 +7n)/2

then we have to find its nth term.

Also we have to write its 20th term.

CBSE DHANPAT RAI publications
Class:- 10th
Solutions of CBSE Mathematics
Question 46

Share

1 Answer

  1. Given Sn = (3n+ 7n) / 2,

    On putting n = 1, we get the first term(a), S1 = a = [3(1)+ 7(1)]/2 = 10/2 = 5

    On putting n = 2 gives S2 = a + a + d = [3(2)+ 7(2)]/2 = 26/2 = 13

    => d = 13 – 2a

    => d = 13 – 10 = 3

    By using the formula of nth term of an A.P.

    an = a + (n – 1)d

    So,

    = 5 + (n – 1)3

    = 5 + 3n – 3

    = 3n + 2

    Now we find the 20th term:

    a20 = 3(20) + 2

    = 60 + 2

    = 62

    Hence, the nth term of the given A.P. is 3n + 2 and the 20th term is 62

    • 0
Leave an answer

Leave an answer

Browse

Choose from here the video type.

Put Video ID here: https://www.youtube.com/watch?v=sdUUx5FdySs Ex: "sdUUx5FdySs".

Captcha Click on image to update the captcha.

Related Questions