KVPY Sample Paper KVPY Stream-SX Model Paper-16

  • question_answer
    If f(x) is a monotonically decreasing function and have concavity up then its inverse \[{{f}^{-1}}(x)\] will be -

    A) decreasing and have concavity upwards

    B) decreasing and have concavity downwards

    C) increasing and have concavity downwards

    D) increasing and have concavity upwards

    Correct Answer: A

    Solution :

    Let \[y=f(x)\]
    \[\therefore {{f}^{-1}}(y)=x\]
    \[\therefore {{f}^{-1}}(y).y'=1\]
    \[{{f}^{-1''}}(y)=-\frac{y'}{{{(y')}^{2}}}\]
    \[\because y'<0\]& \[{y}''>0\]
    \[\therefore {{f}^{-1}}(y)<0\]& \[\therefore {{f}^{-1''}}(y)>0\]


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