Railways R.R.C. (Patna) Solved Paper Held on 2nd Shift 9-11-2014

  • question_answer
    If \[{{a}^{x}}={{b}^{y}}={{c}^{z}}{{b}^{2}}=ac\], then the value of y will be-

    A) \[\frac{xz}{x+z}\]                     

    B) \[\frac{xz}{2(x-z)}\]

    C) \[\frac{xz}{2\,\,(z-x)}\]               

    D) \[\frac{2xz}{(x+z)}\]                   

    Correct Answer: D

    Solution :

    \[{{a}^{x}}={{b}^{y}}={{c}^{z}}=k\] \[a={{k}^{\frac{1}{x}}},\] \[b={{k}^{\frac{1}{y}}},\] \[c={{k}^{\frac{1}{z}}},\] \[{{b}^{2}}=ac\] \[\Rightarrow \]   \[{{({{k}^{\frac{1}{y}}})}^{2}}={{k}^{\frac{1}{x}}}.{{k}^{\frac{1}{z}}}\] \[\Rightarrow \]   \[{{k}^{\frac{2}{y}}}={{k}^{\frac{1}{x}}}+{{k}^{\frac{1}{z}}}\] \[\therefore \]      \[\frac{2}{y}=\frac{1}{x}+\frac{1}{z}\] \[\Rightarrow \]   \[y=\frac{2xz}{x+z}\]


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