RAJASTHAN ­ PET Rajasthan PET Solved Paper-2004

  • question_answer
    The points on the curve\[y=12x-{{x}^{3}}\]at which the slope of the tangent will be zero, are

    A) \[(2,-16),(-2,16)\]  

    B)  (3, 10), (0, 10)

    C)  \[(2,16),(-2,-16)\]  

    D)  None of these

    Correct Answer: C

    Solution :

     Given, curve is \[y=12x-{{x}^{3}}\] Slope \[\frac{dy}{dx}=0\] \[\Rightarrow \]\[12-3{{x}^{2}}=0\] \[\Rightarrow \] \[3{{x}^{2}}=12\]    \[\Rightarrow \]    \[{{x}^{2}}=4\Rightarrow x=\pm 2\] At \[x=+2,\] \[y=24-{{(2)}^{3}}=24-8=16\] At \[x=-2,\] \[y=-24+8=-16\] Hence, required points are (2, 16),\[(-2,-16)\].


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