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Question

Let alpha comma blank beta element of R. If alpha comma blank beta to the power of 2 end exponent be the roots of quadratic equation x to the power of 2 end exponent minus p x plus 1 equals 0 and alpha to the power of 2 end exponent comma beta be the roots of quadratic equation x to the power of 2 end exponent minus q x plus 8 equals 0, then the value of ‘r’ if fraction numerator r over denominator 8 end fraction be arithmetic mean of p and q is

  1. fraction numerator 83 over denominator 2 end fraction   
  2. 83   
  3. fraction numerator 83 over denominator 8 end fraction   
  4. fraction numerator 83 over denominator 4 end fraction  

The correct answer is: 83


    For the equation x to the power of 2 end exponent minus p x plus 1 equals 0,
    The product of roots, alpha beta to the power of 2 end exponent equals 1
    And for the equation x to the power of 2 end exponent minus q x plus 8 equals 0,
    The product of roots alpha to the power of 2 end exponent beta equals 8
    Hence, open parentheses alpha beta to the power of 2 end exponent close parentheses open parentheses alpha to the power of 2 end exponent beta close parentheses equals 8
    rightwards double arrow blank alpha to the power of 3 end exponent beta to the power of 3 end exponent equals 8 blank rightwards double arrow blank alpha beta equals 2
    therefore From alpha beta to the power of 2 end exponent equals 1 comma blankwe haveblank beta equals fraction numerator 1 over denominator 2 end fraction and fromblank alpha to the power of 2 end exponent bullet beta equals 8 comma blankwe haveblank alpha equals 4
    Hence, from sum of roots equals negative fraction numerator b over denominator a end fraction, we have
    p equals alpha plus beta to the power of 2 end exponent equals 4 plus fraction numerator 1 over denominator 4 end fraction equals fraction numerator 17 over denominator 4 end fraction and q equals alpha to the power of 2 end exponent plus beta equals 16 plus fraction numerator 1 over denominator 2 end fraction equals fraction numerator 33 over denominator 2 end fraction
    fraction numerator r over denominator 8 end fraction is arithmetic mean of p and q
    therefore blank fraction numerator r over denominator 8 end fraction equals fraction numerator p plus q over denominator 2 end fraction
    rightwards double arrow r equals 4 open parentheses p plus q close parentheses equals 4 open parentheses fraction numerator 17 over denominator 4 end fraction plus fraction numerator 33 over denominator 2 end fraction close parentheses equals 17 plus 66 equals 83

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