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Chain Rule, Log Differentiation & Rate of Change · Question 94 of 130

Question 94

MediumOriginal question

What is ddx(xlog⁡x)\frac{d}{dx}\left(x^{\log x}\right) for x>0x > 0?

Options for question 94

Show the answer and explanation
CorrectNot quiteAnswer D

Correct answer: D

Explanation

  1. log⁡y=log⁡x⋅log⁡x=(log⁡x)2\log y = \log x \cdot \log x = (\log x)^{2}, so 1ydydx=2log⁡xx\frac{1}{y}\frac{dy}{dx} = \frac{2\log x}{x}.

  2. Multiply back by yy: dydx=xlog⁡x⋅2log⁡xx\frac{dy}{dx} = x^{\log x} \cdot \frac{2\log x}{x}.

Worth noting

log⁡x⋅xlog⁡x−1\log x \cdot x^{\log x - 1} uses the power rule, which needs a constant power; here the power log⁡x\log x varies.

Concept
Logarithmic differentiation
Typical time
90 s
Your time
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The rule this testsLogarithmic differentiation
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Ten questions from Chain Rule, Log Differentiation & Rate of Change, at your own pace.

Practise this chapter →

Ten questions from Chain Rule, Log Differentiation & Rate of Change, at your own pace.