CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • question_answer
    If a is positive and if A and G are the arithmetic mean and the geometric mean of the roots of\[{{x}^{2}}-2ax+{{a}^{2}}=0\]respectively, then

    A)  \[A=G\]              

    B)         \[A=2G\]

    C)  \[2A=G\]        

    D)         \[{{A}^{2}}=G\]

    E)  \[A={{G}^{2}}\]

    Correct Answer: A

    Solution :

    Let\[\alpha \]and\[\beta \]are the roots of the equation \[{{x}^{2}}-2ax+{{a}^{2}}=0.\] \[\therefore \]\[\alpha +\beta =2a\]and \[\alpha \beta ={{a}^{2}}\]                            ...(i) Since, A and G are the arithmetic and geometric mean of the roots. ie,\[A=\frac{\alpha +\beta }{2}\]and \[G=\sqrt{\alpha \beta }\] \[\therefore \]From Eq. (i), \[\frac{\alpha +\beta }{2}=a\]and\[\alpha \beta ={{a}^{2}}\] \[\Rightarrow \]\[A=a\] and\[{{G}^{2}}={{a}^{2}}\] \[\Rightarrow \] \[{{G}^{2}}={{A}^{2}}\Rightarrow G=A\]


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