BCECE Engineering BCECE Engineering Solved Paper-2003

  • question_answer
    If\[x,y,z\] are in GP and \[{{a}^{x}}={{b}^{y}}={{c}^{z}},\]then:

    A) \[{{\log }_{a}}C={{\log }_{b}}a\]

    B)                   \[{{\log }_{b}}a={{\log }_{c}}b\]               

    C)                   \[{{\log }_{c}}b={{\log }_{a}}c\]

    D)                   none of these

    Correct Answer: B

    Solution :

    Since, \[x,y,z\]are in  GP \[\Rightarrow \]               \[{{y}^{2}}=xz\]                ?(i) Now,     \[{{a}^{x}}={{b}^{y}}={{c}^{z}}=m\,(say)\] \[\Rightarrow \]\[x{{\log }_{e}}a=y{{\log }_{e}}=z{{\log }_{e}}c={{\log }_{e}}m\] \[\Rightarrow \]\[x{{\log }_{e}}a={{\log }_{e}}m,y\,{{\log }_{e}}b={{\log }_{e}}m,\]                                 \[z{{\log }_{e}}C={{\log }_{e}}m\] \[\Rightarrow \]\[x={{\log }_{a}}m,y={{\log }_{b}}m,z={{\log }_{c}}m\] From Eq. (i) \[{{y}^{2}}=xz\] \[\Rightarrow \]               \[{{({{\log }_{b}}m)}^{2}}={{\log }_{a}}m{{\log }_{c}}m\] \[\Rightarrow \]               \[\frac{{{\log }_{b}}m}{{{\log }_{a}}m}=\frac{{{\log }_{c}}m}{{{\log }_{b}}m}\] \[\Rightarrow \]               \[{{\log }_{b}}\alpha ={{\log }_{c}}b\]


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