JCECE Engineering JCECE Engineering Solved Paper-2005

  • question_answer
    The point on the curve  \[\sqrt{x}+\sqrt{y}=\sqrt{a}\], the normal at which is parallel to the \[x-\]axis, is:

    A) \[(0,\,\,0)\]                        

    B) \[(0,\,\,a)\]

    C) \[(a,\,\,0)\]                        

    D) \[(a,\,\,a)\]

    Correct Answer: B

    Solution :

    Key Idea: The normal is parallel to \[x-\]axis, if\[\frac{dx}{dy}=0\] Given equation of curve is                 \[\sqrt{x}+\sqrt{y}=\sqrt{a}\]                                    ... (i) On differentiating w.r.t.\[x,\] we get                 \[\frac{1}{2\sqrt{x}}+\frac{1}{2\sqrt{y}}=\frac{dy}{dx}=0\] \[\Rightarrow \]               \[\frac{dx}{dy}=\sqrt{\frac{x}{y}}\] Since, the normal is parallel to\[x-\]axis. \[\therefore \]  \[\frac{dx}{dy}=0\] \[\Rightarrow \]               \[-\sqrt{\frac{x}{y}}=0\]                \[\Rightarrow \]               \[x=0\] \[\therefore \]From Eq. (i)\[y=a\] \[\therefore \]Required point is\[(0,\,\,a)\].


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