Manipal Engineering Manipal Engineering Solved Paper-2012

  • question_answer
    The number of solutions of\[{{\log }_{4}}(x-1)={{\log }_{2}}(x-3)\]is

    A)  3                                            

    B)  1

    C)  2                            

    D)         0

    Correct Answer: B

    Solution :

    \[{{\log }_{4}}(x-1)={{\log }_{2}}(x-3)={{\log }_{{{4}^{1/2}}}}(x-3)\] \[\Rightarrow \]               \[{{\log }_{4}}(x-1)=2{{\log }_{4}}(x-3)\] \[\Rightarrow \]               \[{{\log }_{4}}(x-1)={{\log }_{4}}{{(x-3)}^{2}}\] \[\Rightarrow \]                       \[(x-1)={{(x-3)}^{2}}\]                 \[{{x}^{2}}+9-6x=x-1\] \[\Rightarrow \]       \[{{x}^{2}}-7x+10=0\] \[\Rightarrow \]     \[(x-2)(x-5)=0\] \[\Rightarrow \]      \[x=2\]   or  \[x=5\] Hence,\[x=5\]                    [\[\because \,\,x=2\]makes\[\log (x-3)\]undefined.]


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