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Differentiation question

2023 · 1 Feb · Shift 2 · Q29
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  5. /2023 · 1 Feb · Shift 2 · Q29

Differentiation question

2023 · 1 Feb · Shift 2 · Q29

JEE MainMathematicsDifferentiationMCQ+4 / −1
If y(x)=xx,x>0y(x)=x^{x},x \gt 0y(x)=xx,x>0, then y′′(2)−2y′(2)y''(2)-2y'(2)y′′(2)−2y′(2) is equal to
  1. A
    4(log⁡e2)2+24(\log_{e}2)^{2}+24(loge​2)2+2
  2. B
    8log⁡e2−28\log_{e}2-28loge​2−2
  3. C
    4log⁡e2+24\log_{e}2+24loge​2+2
  4. D
    4(log⁡e2)2−24(\log_{e}2)^{2}-24(loge​2)2−2
View written solutionFree

Correct answer: D

  1. Given function

    y=xx, x>0y=x^x, \, x>0y=xx,x>0

    We need to find:

    y′′(2)−2y′(2)y''(2)-2y'(2)y′′(2)−2y′(2)

  2. Differentiate using logarithmic differentiation

    Let y=xxy=x^xy=xx Taking natural log: ln⁡y=xln⁡x\ln y = x\ln xlny=xlnx

    Differentiate both sides w.r.t. xxx: y′y=ln⁡x+1\frac{y'}{y} = \ln x + 1yy′​=lnx+1

    Hence, y′=y(ln⁡x+1)=xx(ln⁡x+1)y' = y(\ln x+1)=x^x(\ln x+1)y′=y(lnx+1)=xx(lnx+1)

  3. Find second derivative

    Differentiate y′=xx(ln⁡x+1)y'=x^x(\ln x+1)y′=xx(lnx+1)

    Using product rule: y′′=(xx)′(ln⁡x+1)+xx(1x)y'' = (x^x)'(\ln x+1) + x^x\left(\frac{1}{x}\right)y′′=(xx)′(lnx+1)+xx(x1​)

    Since (xx)′=xx(ln⁡x+1),(x^x)'=x^x(\ln x+1),(xx)′=xx(lnx+1), we get y′′=xx(ln⁡x+1)2+xx1xy'' = x^x(\ln x+1)^2 + x^x\frac{1}{x}y′′=xx(lnx+1)2+xxx1​

    So, y′′=xx[(ln⁡x+1)2+1x]y'' = x^x\left[(\ln x+1)^2+\frac{1}{x}\right]y′′=xx[(lnx+1)2+x1​]

  4. Evaluate at x=2x=2x=2

    First, y′(2)=22(ln⁡2+1)=4(ln⁡2+1)y'(2)=2^2(\ln 2+1)=4(\ln 2+1)y′(2)=22(ln2+1)=4(ln2+1)

    Next, y′′(2)=22[(ln⁡2+1)2+12]y''(2)=2^2\left[(\ln 2+1)^2+\frac{1}{2}\right]y′′(2)=22[(ln2+1)2+21​] =4(ln⁡2+1)2+2=4(\ln 2+1)^2+2=4(ln2+1)2+2

  5. Compute y′′(2)−2y′(2)y''(2)-2y'(2)y′′(2)−2y′(2)

    y′′(2)−2y′(2)=[4(ln⁡2+1)2+2]−2⋅4(ln⁡2+1)y''(2)-2y'(2)=\left[4(\ln 2+1)^2+2\right]-2\cdot 4(\ln 2+1)y′′(2)−2y′(2)=[4(ln2+1)2+2]−2⋅4(ln2+1)

    =4(ln⁡2+1)2+2−8(ln⁡2+1)=4(\ln 2+1)^2+2-8(\ln 2+1)=4(ln2+1)2+2−8(ln2+1)

    Expand: 4((ln⁡2)2+2ln⁡2+1)+2−8ln⁡2−84\left((\ln 2)^2+2\ln 2+1\right)+2-8\ln 2-84((ln2)2+2ln2+1)+2−8ln2−8

    =4(ln⁡2)2+8ln⁡2+4+2−8ln⁡2−8=4(\ln 2)^2+8\ln 2+4+2-8\ln 2-8=4(ln2)2+8ln2+4+2−8ln2−8

    =4(ln⁡2)2−2=4(\ln 2)^2-2=4(ln2)2−2

  6. Match with options

    4(log⁡e2)2−24(\log_e 2)^2-24(loge​2)2−2

    This is Option D.

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