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JEE Mains · Maths · STD 12 - 8. Application and integration

माना \(S (\alpha)=\left\{( x , y ): y ^{2} \leq x , 0 \leq x \leq \alpha\right\}\) तथा \(A (\alpha)\) क्षेत्र \(S(\alpha)\) का क्षेत्रफल है। यदि किसी \(\lambda, 0<\lambda<4\) के लिए \(A (\lambda): A (4)=2: 5\) है, तो \(\lambda\) बराबर है

  1. A \(4{\left( {\frac{2}{5}} \right)^{\frac{1}{3}}}\)
  2. B \(2{\left( {\frac{2}{5}} \right)^{\frac{1}{3}}}\)
  3. C \(4{\left( {\frac{4}{25}} \right)^{\frac{1}{3}}}\)
  4. D \(2{\left( {\frac{4}{25}} \right)^{\frac{1}{3}}}\)
Verified Solution

Answer & Solution

Correct Answer

(C) \(4{\left( {\frac{4}{25}} \right)^{\frac{1}{3}}}\)

Step-by-step Solution

Detailed explanation

\(S\left( \lambda \right) = 2\int\limits_0^\lambda {\sqrt x dx = \frac{4}{3}} {\lambda ^{3/2}}\) \(\frac{S(\lambda)}{S(4)}=\frac{2}{5} \Rightarrow \frac{\lambda^{3 / 2}}{4^{3 / 2}}=\frac{2}{5}\) \(\Rightarrow \lambda=4\left(\frac{4}{25}\right)^{1 / 3}\)
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