KVPY Sample Paper KVPY Stream-SX Model Paper-15

  • question_answer
    The number of values of \[k\] for which \[[{{x}^{2}}-(k-2)x+{{k}^{2}}]\,\,\,[{{x}^{2}}+kx+(2k-1)]\] is a perfect square is -

    A) 1

    B) 2

    C) 0

    D) none of these

    Correct Answer: A

    Solution :

    \[{{x}^{2}}-(k-2)\,\,x+{{k}^{2}}=0\]
    \[{{x}^{2}}+kx-2k-1=0\] should have both roots. Common or each should have equal roots.
    Case. (i) \[\frac{1}{1}=\frac{-\,(k-2)}{k}=\frac{{{k}^{2}}}{2k-1}\]
    \[\Rightarrow k=-\,k+2\] and \[2k-1={{k}^{2}}\]
    \[\Rightarrow k=1\]
    Case. (ii) \[{{(k-2)}^{2}}-4{{k}^{2}}=0\] and \[{{k}^{2}}-4(2k-1)=0\]
    \[(3k-2)(-\,k-2)=0\] and \[{{k}^{2}}-8k+4=0\] have no common value, \[k=1\] is the only solution.


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