JEE Main & Advanced Mathematics Functions Question Bank Self Evaluation Test - Relations and Functions-I

  • question_answer
    A function f is defined by \[f(x)=x+\frac{1}{x}.\] Consider the following.
    (1) \[{{(f(x))}^{2}}=f({{x}^{2}})+2\]
    (2) \[{{(f(x))}^{3}}=f({{x}^{3}})+3f(x)\]
    Which of the above is/are correct?

    A) (1) only

    B)        (2) only

    C) Both (1) and (2)

    D)                    Neither (1) nor (2)

    Correct Answer: C

    Solution :

    [c] \[f({{x}^{2}})+2={{x}^{2}}+\frac{1}{{{x}^{2}}}+2\] \[={{\left( x+\frac{1}{x} \right)}^{2}}={{\{f(x)\}}^{2}}\] And \[f({{x}^{3}})+3f(x)\] \[={{x}^{3}}+\frac{1}{{{x}^{3}}}+3\left( x+\frac{1}{x} \right)\] \[={{\left( x+\frac{1}{x} \right)}^{3}}={{\{f(x)\}}^{3}}\] Thus, both 1 and 2 are correct.


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