
Last updated at Dec. 8, 2016 by Teachoo
Transcript
Ex 9.3,7 Find the sum to 20 terms in the geometric progression 0.15, 0.015, 0.0015 โฆ 0.15, 0.015, 0.0015 โฆ We know that Sn = (a(1 โ ๐^๐))/(1 โ r) where Sn = sum of n terms of GP n is the number of terms a is the first term r is the common ratio First term a = 0.15 , Common ratio r = 0.015/0.15 ` = 15/1000 ร 100/15 = 1/10 We know that Sum of n term = (๐(1 โ ๐^๐))/(1 โ ๐) We need to find sum of 20 terms. S20 = (๐(1 โ ๐^20))/(1 โ ๐) We need to find sum of 20 terms, we use the formula Sn = (a(1 โ ๐^๐))/(1 โ r) Putting a = 0.15, r = 0.1,n=20 S20 = (0.15(1 โ(0.1)20))/(1 โ 0.1) S20 =(0.15(1 โ(0.1)20))/0.9 S20 = 1/6[ 1 โ (0.1)20] Hence, sum of 20 terms of GP is 1/6[ 1 โ (0.1)20]
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