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1. Find the sum of the …

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1. Find the sum of the sequence 7,77,777,7777,......to n terms. Please give a detailed explanation

    • Posted by Jaya Jeevan 3 years, 6 months ago

    CBSE > Class 11 > Mathematics
    • 1 answers

    Gaurav Seth 3 years, 6 months ago

    7, 77, 777, 7777 ….to n terms.         
    Sn=7+77+777+7777+……+to n terms      
    introducing 9       
      = (7/9) [9+99+999+……+ to n terms]              
    = (7/9) [(10-1) + (100-1) + (1000-1) +……...+ to n term]               
    = (7/9) [10+100+1000+……... n terms – (1+1+1+1+…… n terms)             
      = (7/9) [10+100+1000+………n terms –n]     
     Here      a=10, r=10             
     = (7/9) [10(10n-1)/ (9) - n]

    1Thank You

    ANSWER
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