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Question

The sum of the series 1.3 to the power of 2 end exponent plus 2.5 to the power of 2 end exponent plus 3.7 to the power of 2 end exponent plus blank... upto 20 terms is

  1. 188090    
  2. 189080    
  3. 199080    
  4. 199089    

The correct answer is: 188090


    Here, T subscript n end subscript o f blank t h e A P blank 12 comma 3 horizontal ellipsis equals n
    andT subscript n end subscriptof the AP 35 comma 7 horizontal ellipsis equals 2 n plus 1
    therefore T subscript n end subscriptof given seriesequals n open parentheses 2 n plus 1 close parentheses 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
    Hence, S equals not stretchy sum subscript n equals 1 end subscript superscript 20 end superscript T subscript n end subscript equals 4 not stretchy sum subscript n equals 1 end subscript superscript 20 end superscript n to the power of 3 end exponent plus 4 not stretchy sum subscript n equals 1 end subscript superscript 20 end superscript n to the power of 2 end exponent plus not stretchy sum subscript n equals 1 end subscript superscript 20 end superscript n
    equals 4 fraction numerator 1 over denominator 4 end fraction 20 to the power of 2 end exponent.21 to the power of 2 end exponent plus 4 fraction numerator 1 over denominator 6 end fraction 20.21.41+fraction numerator 1 over denominator 2 end fraction 20.21
    equals 188090

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