Check sibling questions

Ex 9.4, 6 - Find sum 3 x 8 + 6 x 11 + 9 x 14 - Chapter 9 Class 11 - Finding sum from nth number

Ex 9.4, 6 - Chapter 9 Class 11 Sequences and Series - Part 2
Ex 9.4, 6 - Chapter 9 Class 11 Sequences and Series - Part 3

This video is only available for Teachoo black users

Solve all your doubts with Teachoo Black (new monthly pack available now!)


Transcript

Ex 9.4, 6 Find the sum to n terms of the series 3 8 + 6 11 + 9 14 + Step 1: Finding nth term an an = (nth term of 3, 6, 9 ) (nth term of 8, 11, 14, ) an = (3n)(3n + 5) = 9n2 + 15n Step 2: Finding sum of n terms = 9 (n(n+1)(2n+1))/6 +15 (n(n+1))/2 = 9 ( + 1)(2 + 1)/6 + (15 ( + 1))/2 = (3n(n+1)(2n+1))/2 + (15n(n+1))/2 = (3n(n+1))/2 [(2n+1)+5] = (3n(n+1))/2 [2n+1+5] = (3n(n+1))/2 [2n+6] = 3/2n(n+1) 2(n+3) = 3n(n + 1)(n + 3) Hence, The required sum is 3n(n + 1)(n + 3)

Davneet Singh's photo - Co-founder, Teachoo

Made by

Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.