JEE Main & Advanced Sample Paper JEE Main - Mock Test - 9

  • question_answer
    If \[{{a}^{x}}=bc,\] \[{{b}^{y}}=ca\] and \[{{c}^{2}}=ab,\] where a, b, c are positive numbers different from unity, then the value of \[\frac{x}{1+x}+\frac{y}{1+y}+\frac{z}{1+z}\] is

    A) \[1/2\]         

    B) \[1\]                       

    C) \[2\]      

    D) \[1/3\]

    Correct Answer: C

    Solution :

    [c] \[{{a}^{x}}=bc,\] \[{{b}^{y}}=ca,\] \[{{c}^{z}}=ab\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,x={{\log }_{a}}bc,\,\,y={{\log }_{b}}ac,\,\,z={{\log }_{c}}ab\] \[\Rightarrow \,\,\,\,\,\,\,\,\frac{x}{1+x}+\frac{y}{1+y}+\frac{z}{1+z}=\frac{{{\log }_{a}}bc}{{{\log }_{a}}abc}+\frac{{{\log }_{b}}ac}{{{\log }_{b}}abc}\] \[+\frac{{{\log }_{c}}ab}{{{\log }_{c}}abc}\]             \[={{\log }_{abc}}bc+{{\log }_{abc}}ac+{{\log }_{abc}}ab\]             \[={{\log }_{abc}}{{(abc)}^{2}}=2\]          


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