ICSE Class 10CISCE
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Q 1.3 - ICSE Class 10 - Mathematics

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Question

Q 1.3

Solution

Given G.P. : `1-1/2+1/4-1/8+......`
Here,
first term, a = 1
common ratio, r = `(-1/2)/1=-1/2` (r < 1)
number of terms to be added, n = 9

`therefore "S"_n=(a(1-r^n))/(1-r)`

⇒ S8 = `(1(1-(-1/2)^9))/(1-(-1/2))`

`=(1-(-1/2)^9)/(1+1/2)`

`=(1+1/2^9)/(3/2)`

`=2/3(1+1/2^9)`

`=2/3(1+1/512)`

`=2/3xx513/512`

`=171/256`

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Solution Q 1.3 Concept: Simple Applications - Geometric Progression.
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