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Ex 9.4, 9 - Find sum of series, nth term is n2 + 2n - Class 11 - Finding sum from nth number

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

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Ex 9.4, 9 Find the sum to n terms of the series whose nth terms is given by n2 + 2n Given an = n2 + 2n Now, sum of n terms is Now, = 2 + 4 + 8 + + 2n This is GP with first term A = 2 & common ratio R = 4/2 = 2 We know that sum of n term in GP Sn = ( (R^n 1))/(R 1) Putting values Now from (1) Putting values = (n(n+1)(2n+1))/6 + 2(2n 1) Thus, the required sum is (n(n+1)(2n+1))/6 + 2(2n 1)

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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.