10th Class Mathematics Related to Competitive Exam Question Bank Algebra

  • question_answer
    If \[{{\log }_{10}}a+{{\log }_{10}}b={{\log }_{10}}(a+b)\], then

    A)  \[a=b=2\]         

    B) \[~\text{a}=\text{b}=\text{1}\]

    C)  \[a=\frac{{{b}^{2}}}{1-b}\]         

    D)         \[a=\frac{b}{b-1}\]  

    Correct Answer: D

    Solution :

     Since\[{{\log }_{10}}a+{{\log }_{10}}b={{\log }_{10}}(a+b)\] \[\therefore \]  \[{{\log }_{10}}a\times b={{\log }_{10}}(a+b)\] \[\Rightarrow \]               \[ab=a+b\] \[\Rightarrow \]               \[ab-a=b\] \[\Rightarrow \]               \[a(b-1)=b\] \[\Rightarrow \]               \[a=\frac{b}{(b-1)}\]


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