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JEE Main 202522 JanuaryEvening Shift
Exam
JEE Main
Year
2025
Date
22 January
Shift
Evening Shift
Subject
Mathematics
Chapter
Limits

JEE Main 2025 · 22 January · Evening Shift · Mathematics · Limits

If _ x arrow ∞ (( e 1-e )( 1 e -(x)/(1+x)))^x=α , then the value of...

If lim⁡x→∞((e1−e)(1e−x1+x))x=α\lim _{x \rightarrow \infty}\left(\left(\frac{\mathrm{e}}{1-\mathrm{e}}\right)\left(\frac{1}{\mathrm{e}}-\frac{x}{1+x}\right)\right)^x=\alpha, then the value of log⁡eα1+log⁡eα\frac{\log _{\mathrm{e}} \alpha}{1+\log _{\mathrm{e}} \alpha} equals :

Options

  1. Ae−1e^{-1}
  2. Be2\mathrm{e}^2
  3. Ce−2e^{-2}
  4. De

Correct answer

D. e

Step-by-step solution

α=lim⁡x→∞((e1−e)(1e−x1+x))x(1∞ form )∴α=eL Where L=lim⁡x→∞x((e1−e)(1e−x1+x)−1)⇒L=lim⁡x→∞(e1−e)x(1e−x1+x−(1−ee))⇒L=e1−elim⁡x→∞x(1−x1+x)⇒L=e1−elim⁡x→∞xx+1⇒L=e1−e⋅1⇒L=e1−e∴α=ee1−e⇒log⁡α=e1−e∴ Required value =e1−e1+e1−e=e\begin{aligned} & \alpha=\lim _{x \rightarrow \infty}\left(\left(\frac{\mathrm{e}}{1-\mathrm{e}}\right)\left(\frac{1}{\mathrm{e}}-\frac{\mathrm{x}}{1+\mathrm{x}}\right)\right)^{\mathrm{x}}\left(1^{\infty} \text{ form }\right) \\ & \therefore \alpha=\mathrm{e}^{\mathrm{L}} \\ & \text{ Where } \mathrm{L}=\lim _{x \rightarrow \infty} \mathrm{x}\left(\left(\frac{\mathrm{e}}{1-\mathrm{e}}\right)\left(\frac{1}{\mathrm{e}}-\frac{\mathrm{x}}{1+\mathrm{x}}\right)-1\right) \\ & \Rightarrow \mathrm{L}=\lim _{\mathrm{x} \rightarrow \infty}\left(\frac{\mathrm{e}}{1-\mathrm{e}}\right) \mathrm{x}\left(\frac{1}{\mathrm{e}}-\frac{\mathrm{x}}{1+\mathrm{x}}-\left(\frac{1-\mathrm{e}}{\mathrm{e}}\right)\right) \\ & \Rightarrow \mathrm{L}=\frac{\mathrm{e}}{1-\mathrm{e}} \lim _{\mathrm{x} \rightarrow \infty} \mathrm{x}\left(1-\frac{\mathrm{x}}{1+\mathrm{x}}\right) \\ & \Rightarrow \mathrm{L}=\frac{\mathrm{e}}{1-\mathrm{e}} \lim _{\mathrm{x} \rightarrow \infty} \frac{\mathrm{x}}{\mathrm{x}+1} \\ & \Rightarrow \mathrm{ L}=\frac{\mathrm{e}}{1-\mathrm{e}} \cdot 1 \\ & \Rightarrow \mathrm{ L}=\frac{\mathrm{e}}{1-\mathrm{e}} \\ & \therefore \alpha=\mathrm{e}^{\frac{\mathrm{e}}{1-\mathrm{e}}} \Rightarrow \log \alpha=\frac{\mathrm{e}}{1-\mathrm{e}} \\ & \therefore \text{ Required value }=\frac{\frac{\mathrm{e}}{1-\mathrm{e}}}{1+\frac{\mathrm{e}}{1-\mathrm{e}}}=\mathrm{e}\end{aligned}
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