BCECE Engineering BCECE Engineering Solved Paper-2015

  • question_answer
    106.        Let \[f:R\to R\] be a function defined by \[f(x)=\frac{{{x}^{2}}-8}{{{x}^{2}}+2}.\] Then, \[f\] is

    A)                 one-one but not onto

    B) one-one and onto

    C) onto but not one-one

    D) neither one-one nor onto

    Correct Answer: D

    Solution :

    We have, \[f(x)=\frac{{{x}^{2}}-8}{{{x}^{2}}+2}\] Clearly, \[f(-x)=f(x)\]. Therefore, \[f\] is not one-one. Again, \[f(x)=\frac{{{x}^{2}}-8}{{{x}^{2}}+2}=1-\frac{10}{{{x}^{2}}+2}\] \[\Rightarrow \]               \[f(x)<1\]for all \[x\in R\] \[\Rightarrow \]Range of f \[\ne \]codomain of f, i.e.R So, f is not onto. Hence, f is neither one-one nor onto.


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