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Question 7 - Examples - Chapter 8 Class 11 Sequences and Series

Last updated at May 29, 2023 by

Example 20 - Find sum to n terms of series, nth term is n(n + 3) - Finding sum from nth number

Example 20 - Chapter 9 Class 11 Sequences and Series - Part 2

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Question 7, Find the sum to n terms of the series whose nth term is n (n+3). Given an = n (n + 3) = n2 + 3n The sum of n terms is = (n( n + 1)(2n + 1))/6 + (3n( n + 1) )/2 = (n(n + 1))/2 (( (2n + 1))/3 " + 3" ) = (n(n + 1))/2 (( (2n + 1) + 9)/3) = (n(n+1))/2 × (( 2𝑛 +10 )/3) = (n(n+1))/2 × ( 2(𝑛 +5) )/3 = (n( n + 1)(n + 5) )/3 Thus, the required sum is (n( n + 1)(n + 5) )/3

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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.