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Question

The sum of the series 1 times 3 to the power of 2 end exponent plus 2 times 5 to the power of 2 end exponent plus 3 times 7 to the power of 2 end exponent plus midline horizontal ellipsisup to 20 terms is

  1. 188090    
  2. 189080    
  3. 199080    
  4. None of these    

The correct answer is: 188090


    text Here  end text T subscript n end subscript text  of the AP  end text 12 comma 3 comma midline horizontal ellipsis equals n
    And T subscript n end subscript of the AP 3, 5, 7, … = 2n+1
    Therefore,
    T subscript n end subscript text  of given series  end text equals n left parenthesis 2 n plus 1 right parenthesis to the power of 2 end exponent equals 4 n to the power of 3 end exponent plus 4 n to the power of 2 end exponent plus n
    text Hence,  end text S equals stretchy sum from 1 to 20 of   T subscript n end subscript equals 4 stretchy sum from 1 to 20 of   n to the power of 3 end exponent plus 4 stretchy sum from 1 to 20 of   n to the power of 2 end exponent plus stretchy sum from 1 to 20 of   n
    equals 4 times fraction numerator 1 over denominator 4 end fraction 20 to the power of 2 end exponent times 21 to the power of 2 end exponent plus 4 times fraction numerator 1 over denominator 6 end fraction 20 times 21 times 41 plus fraction numerator 1 over denominator 2 end fraction 20 times 21 equals 188090

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