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Misc 22 - Find 20th term of series 2 x 4 + 4 x 6 + 6 x 8 - Finding sum from nth number

Misc 22 - Chapter 9 Class 11 Sequences and Series - Part 2

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Misc 22 Find the 20th term of the series 2 × 4 + 4 × 6 + 6 × 8 + … + n terms. Now, an = [nth term of 2, 4, 6 …] × [nth term of 4, 6, 8 …] = (2n) (2n + 2) = (2n) (2(n + 1)) = 4n (n + 1) Thus, nth term of series 2 × 4 + 4 × 6 + 6 × 8… is an = 4n (n + 1) We need to find 20th term of given series Putting n = 20 a20 = 4 × 2(20 + 1) = 80 (21) = 1680 Hence 20th term of series is 1680

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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.