Ex 8.2

Chapter 8 Class 11 Sequences and Series
Serial order wise

### Transcript

Ex 8.2, 17 If the 4th, 10th and 16th terms of a G.P. are x, y and z, respectively. Prove that x, y, z are in G.P. We know that an = arn 1 where an = nth term of GP n is the number of terms a is the first term r is the common ratio Here, 4th term is x i.e. a4 = x Putting n = 4 in an formula x = ar4 1 x = ar3 Also, 10th term is y i.e. a10 = y Putting n = 10 in an formula y = ar10 1 y = ar9 Also, 16th term is z i.e. a16 = z Putting n = 16 in an formula z = ar16 1 z = ar15 We need to show x, y, z are in GP i.e. we need to show / = / Calculating / / Putting y = ar9 & x = ar3 = 9/ 3 = r9 3 = r6 Now calculating / / putting z = ar15 & y = ar9 = 15/ 9 = r15 9 = r6 Thus, / = r6 , & / = r6 Hence / = / x, y, z are in G.P Hence proved

#### Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.