KVPY Sample Paper KVPY Stream-SX Model Paper-26

  • question_answer
    The function \[f:\left[ 0,3 \right]\to \left[ 1,29 \right]\], defined by is \[f\left( x \right)=2{{x}^{3}}-15{{x}^{2}}+36x+1\]

    A) one-one and onto     

    B) onto but not one-one

    C) one-one but not onto  

    D) neither one-one nor onto

    Correct Answer: B

    Solution :

    We have, \[f\left( x \right)=2{{x}^{3}}-15{{x}^{2}}+36x+1\] \[\Rightarrow f'\left( x \right)=6{{x}^{2}}-30x+36\] \[\Rightarrow f'\left( x \right)=6\left( x-2 \right)\left( x-3 \right)\] f(x) is increasing in [0, 2] and decreasing in [2, 3]. f (x) is many one \[f\left( 0 \right)=1,f\left( 2 \right)=29,f\left( 3 \right)=28\] Range = [1, 29] f(x) is onto but not one-one.


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