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प्रश्न
Q 10.3
बेरीज
उत्तर
Required sum = 2 + 22 + 222 +..........upto n terms
= 2(1 + 11 + 111 +..........upto n terms
=`2/9`(9 + 99 + 999 +..........upto n terms
=`2/9`[(10 - 1) + (100 - 1) +(1000 - 1) +..........upto n terms]
=`2/9`[(10 + 102 + 103 +..........upto n terms) - (1 + 1 + 1 +..........upto n terms)]
`=2/9[(10(10^n-1))/(10-1)-"n"]`
`=2/9[10/9(10^n-1)-"n"]`
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Geometric Progression - Finding Sum of Their First ‘N’ Terms
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