JEE Main & Advanced Sample Paper JEE Main Sample Paper-18

  • question_answer
    If a variable tangent to the curve \[{{x}^{2}}y={{c}^{3}}\]makes intercepts \[a\] and \[b\] on \[x\] and \[y\] axis, respectively, then the value of\[{{a}^{2}}b\]is

    A)  \[27\,{{c}^{3}}\]                              

    B)  \[\frac{4}{27}{{c}^{3}}\]

    C)  \[\frac{27}{4}{{c}^{3}}\]                              

    D)  \[\frac{4}{9}{{c}^{3}}\]

    Correct Answer: C

    Solution :

     Given curve is\[{{x}^{2}}y={{c}^{3}}\]. Differentiating w.r.t. \[x,\]we get \[{{x}^{2}}\frac{dy}{dx}+2xy=0\] \[\Rightarrow \]               \[\frac{dy}{dx}=-\frac{2y}{x}=-\frac{2y}{x}\] So, equation of tangent at\[(x,y)\]is: \[Y-y=-\frac{2y}{x}(X-x)\] \[Y=0,\]gives, \[X=\frac{3x}{2}=a\] and \[X=0,\]gives, \[Y=3y=b\] Now, \[{{a}^{2}}b=\frac{9{{x}^{2}}}{4}\cdot 3y=\frac{27}{4}{{x}^{2}}y=\frac{27}{4}{{c}^{3}}\]


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