JEE Main & Advanced JEE Main Paper (Held on 08-4-2019 Afternoon)

  • question_answer
    Let\[S(\alpha )=\{(x,y):{{y}^{2}}\le x,0\le x\le \alpha \}\] and \[A(\alpha )\]is area of the region \[S(\alpha )\]. If for a \[\lambda ,0<\lambda <4,A(\lambda ):A(4)=2:5,\]then \[\lambda \] equals [JEE Main 8-4-2019 Afternoon]

    A) \[2{{\left( \frac{4}{25} \right)}^{\frac{1}{3}}}\]               

    B) \[4{{\left( \frac{4}{25} \right)}^{\frac{1}{3}}}\]

    C) \[2{{\left( \frac{2}{5} \right)}^{\frac{1}{3}}}\]     

    D)   \[4{{\left( \frac{2}{5} \right)}^{\frac{1}{3}}}\]

    Correct Answer: B

    Solution :

    \[S(\alpha )=\{(x,y):{{y}^{2}}\le x,0\le x\le \alpha \}\]           \[A(\alpha )=2\int\limits_{0}^{\alpha }{\sqrt{x}}dx=2{{\alpha }^{\frac{3}{2}}}\]           \[A(4)=2\times {{4}^{3/2}}=16\]           \[A(\lambda )=2\times {{\lambda }^{3/2}}\]           \[\frac{A(\lambda )}{A(4)}=\frac{2}{5}\Rightarrow \lambda =4.{{\left( \frac{4}{25} \right)}^{1/3}}\]


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