Check sibling questions

Ex 9.3, 15 - Given a GP with a = 729 and 7th term 64 - Ex 9.3

Ex 9.3, 15 - Chapter 9 Class 11 Sequences and Series - Part 2
Ex 9.3, 15 - Chapter 9 Class 11 Sequences and Series - Part 3


Transcript

Ex9.3, 15 Given a G.P. with a = 729 and 7th term 64, determine S7. First term a = 729 and 7th term = 64 we know that nth term of G.P. = arn-1 a7 = ar6 putting values 64 = 729 r6 64/729 = r6 2^6/3^6 = r6 (2/3)^6= r6 (2/3)^6= r6 Comparing powers r = 2/3 We need to find sum of first 7 terms We know that Sum of n terms = (1 ^ )/(1 ) Sn = (1 ^ )/(1 ) S7 = (1 7)/(1 ) Putting values S7 = 729(1 (2/3)^7 )/(1 2/3) S7 = 729(1 (2/3)^7 )/(1 2/3) S7 = 729(1 128/2187)/((3 2)/3) S7 = 729(1 128/2187)/(1/3) S7 = 729(2059/2187) 3 S7 = 2187(2059/2187) S7 = 2059 Hence S7 = 2059 Hence, sum of first 7 terms is 2059

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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.