JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Tangent and Normal

  • question_answer
    The equation of the tangent to the curve \[(1+{{x}^{2}})y=2-x,\] where it crosses the x-axis, is                                    [Kerala (Engg.) 2002]

    A)            \[x+5y=2\]

    B)            \[x-5y=2\]

    C)            \[5x-y=2\]

    D)            \[5x+y-2=0\]

    Correct Answer: A

    Solution :

               \[(1+{{x}^{2}})y=2-x\]                       ......(i)            It meets x-axis, where \[y=0\] i.e., \[0=2-x\Rightarrow x=2\]            So, (i) meets x-axis at the point (2, 0)            Also from (i), \[y=\frac{2-x}{1+{{x}^{2}}}\]            Þ \[\frac{dy}{dx}=\frac{(1+{{x}^{2}})\,(-1)-(2-x)\,(2x)}{{{(1+{{x}^{2}})}^{2}}}\]Þ \[\frac{dy}{dx}=\frac{{{x}^{2}}-4x-1}{{{(1+{{x}^{2}})}^{2}}}\]            Slope of tangent at (2, 0)is,\[\frac{4-8-1}{{{(1+4)}^{2}}}=\frac{-5}{25}=\frac{-1}{5}\]            \ Equation of tangent at (2, 0) is ,            \[y-0=-\frac{1}{5}(x-2)\Rightarrow x+5y=2\].


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