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Differentiation question

2004 · Shift 0 · Q77
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Differentiation question

2004 · Shift 0 · Q77

JEE MainMathematicsDifferentiationMCQ+4 / −1
If x=ey+ey+ey+.....∞x = {e^{y + {e^y} + {e^{y + .....\infty }}}}x=ey+ey+ey+.....∞, x>0,x \gt 0,x>0, then dydx{{{dy} \over {dx}}}dxdy​ is
  1. A
    1+xx{{1 + x} \over x}x1+x​
  2. B
    1x{1 \over x}x1​
  3. C
    1−xx{{1 - x} \over x}x1−x​
  4. D
    x1+x{x \over {1 + x}}1+xx​
View written solutionFree

Correct answer: C

  1. Interpret the infinite expression

    Given x = e^{y + e^y + e^{y + rac{}{} ext{continuing infinitely}}}

    The repeating part after y+y+y+ is again the whole exponent structure. Hence we can write x=ey+x.x = e^{y + x}.x=ey+x.

  2. Take natural logarithm

    Since x>0x>0x>0, taking ln\\lnln on both sides is valid: ln⁡x=y+x.\ln x = y + x.lnx=y+x.

  3. Express yyy in terms of xxx

    y=ln⁡x−x.y = \ln x - x.y=lnx−x.

  4. Differentiate with respect to xxx

    dydx=ddx(ln⁡x−x)=1x−1.\frac{dy}{dx} = \frac{d}{dx}(\ln x - x) = \frac{1}{x} - 1.dxdy​=dxd​(lnx−x)=x1​−1.

    Simplifying, dydx=1−xx.\frac{dy}{dx} = \frac{1-x}{x}.dxdy​=x1−x​.

  5. Match with the options

    1−xx\frac{1-x}{x}x1−x​ corresponds to Option C.


Verification with stored answer: Stored correct answer is C, which matches our derived answer.

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