1.

Differentiate x^3e^x with respect to x.(a) 3e^3x (3 log⁡x+\(\frac{1}{x}\))(b) x^3e^3x.3e^3x (3 log⁡x-\(\frac{1}{x}\))(c) x^3e^3x (3 log⁡x+\(\frac{1}{x}\))(d) x^3e^3x.3e^3x (3 log⁡x+\(\frac{1}{x}\))I got this question in a job interview.My question is taken from Logarithmic Differentiation topic in section Continuity and Differentiability of Mathematics – Class 12

Answer»

Right choice is (d) x^3e^3x.3e^3x (3 log⁡x+\(\FRAC{1}{x}\))

For EXPLANATION: CONSIDER y=x^3e^3x

Applying log on both sides, we get

log⁡y=3e^3x log⁡x

Differentiating both sides with respect to x, we get

\(\frac{1}{y} \frac{dy}{dx} = \frac{d}{dx} (3e^{3x}) log⁡x+\frac{d}{dx} (log⁡x)3e^{3x}\)

\(\frac{1}{y} \frac{dy}{dx}\)=3e^3x.3.log⁡x+\(\frac{1}{x}\) 3e^3x

\(\frac{dy}{dx}\)=y(3e^3x.3.log⁡x+\(\frac{1}{x}\) 3e^3x)

\(\frac{dy}{dx}\)=x^3e^3x.3e^3x (3 log⁡x+\(\frac{1}{x}\))



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