Example 14 - Sum of first three terms of GP is 13/12, product

Example 14 - Chapter 9 Class 11 Sequences and Series - Part 2
Example 14 - Chapter 9 Class 11 Sequences and Series - Part 3
Example 14 - Chapter 9 Class 11 Sequences and Series - Part 4
Example 14 - Chapter 9 Class 11 Sequences and Series - Part 5
Example 14 - Chapter 9 Class 11 Sequences and Series - Part 6
Example 14 - Chapter 9 Class 11 Sequences and Series - Part 7
Example 14 - Chapter 9 Class 11 Sequences and Series - Part 8

  1. Chapter 9 Class 11 Sequences and Series (Term 1)
  2. Serial order wise

Transcript

Example 14 The sum of first three terms of a G.P. is 13/12 and their product is – 1. Find the common ratio and the terms. Let the three terms in G.P. be 𝑎/𝑟, a, ar here 1st term of G.P. = 𝑎/𝑟 2nd term of G.P. = a 3rd term of G.P. = ar It is given that Sum of first three terms of G.P. = 13/12 i.e. a/r + a + ar = 13/12 (− 1 −r −r2)/r = 13/12 12( -1 – r – r2 )= 13r -12 – 12r – 12r2 = 13r -12 - 12r - 12r2 – 13r = 0 -12 - 25r - 12r2 = 0 -(12 + 25r + 12r2)= 0 12r2 + 25r + 12= 0 This equation is of the form ax2 + bx + c = 0 where a = 12 b = 25 c = 12 & x = r

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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 10 years. He provides courses for Maths and Science at Teachoo.