J & K CET Engineering J and K - CET Engineering Solved Paper-2008

  • question_answer
    The function \[f:R\to R\] given by \[f(x)={{x}^{3}}-1\] is

    A)  a one-one function

    B)  an onto function

    C)  a bijection

    D)  neither one-one nor onto

    Correct Answer: C

    Solution :

    Given,   \[f(x)=\,{{x}^{3}}-1\] Let \[{{x}_{1}}\,,\,{{x}_{2}}\,\in \,R.\] Now, \[f({{x}_{1}})=f({{x}_{2}})\] \[\Rightarrow \] \[x_{1}^{3}-1=x_{2}^{3}-1\] \[\Rightarrow \] \[x_{1}^{3}=x_{2}^{3}\,\,\,\Rightarrow \,\,\,{{x}_{1}}={{x}_{2}}\] \[\therefore \] \[f(x)\]  is one-one. Also,  it is onto. Hence, it is a bisection.


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