Railways Quantitative Aptitude Power, Surds And Indices Sample Paper Surds Indices Sample Test Paper-4

  • question_answer
    If abc = 1, then \[\left( \frac{1}{1+a+{{b}^{-1}}}+\frac{1}{1+b+{{c}^{-1}}}+\frac{1}{1+c+{{a}^{-1}}} \right)=?\]

    A)  0                    

    B)  1         

    C)  \[\frac{1}{ab}\]            

    D)  ab

    Correct Answer: B

    Solution :

    [b] Given Exp. \[=\frac{1}{1+a+{{b}^{-1}}}+\frac{1}{1+b+{{c}^{-1}}}+\frac{1}{1+c+{{a}^{-1}}}\] \[=\frac{1}{1+a+{{b}^{-1}}}+\frac{{{b}^{-1}}}{1+{{b}^{-1}}{{c}^{-1}}+{{b}^{-1}}}+\frac{1}{a+ac+1}\] \[=\frac{1}{1+a+{{b}^{-1}}}+\frac{{{b}^{-1}}}{1+{{b}^{-1}}+a}+\frac{1}{a+{{b}^{-1}}+1}\] \[=\frac{1+a+{{b}^{-1}}}{1+a+{{b}^{-1}}}=1\] \[\because \] \[abc=1\] \[\Rightarrow \] \[{{(bc)}^{-1}}=a\] \[\Rightarrow \] \[{{b}^{-1}}{{c}^{-1}}=a\,\,and\,\,ac={{b}^{-1}}\]


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