Finding Sequences

Chapter 9 Class 11 Sequences and Series
Concept wise

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### Transcript

Ex9.1 , 5 Write the first five terms of the sequences whose nth term is an = (-1)n 1 5n + 1 We need to find first five terms i.e. a1, a2, a3 , a4, a5 Let an = (-1)n 1 5n + 1 Putting n = 1 in (1) a1 = (-1)1 1 51 + 1 = (-1)0 52 = 1 52 = 5 5 = 25 Putting n = 2 in (1) a2 = (-1)2 1 52 + 1 = (-1)1 53 = (-1) (5 5 5) = -1(125) = -125 Putting n = 3 in (1) a3 = (-1)3 1 53 + 1 = (-1)2 54 = 1 54 = (5 5 5 5) = 625 Putting n = 4 in (1) a4 = (-1) 4 1 54 + 1 = (-1) 3 (5)5 = (-1)(5)5 = (-1) (5 5 5 5 5) = -1(3125) = -3125 Putting n = 5 in (1) a5 = (-1)5 1 55 + 1 = (-1)4 (5)6 = 1 56 = 1 (5 5 5 5 5 5) = 15625 Hence first five terms are 25, 125, 625, 3125, and 15625.

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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.