Class CBSE Class 12 Mathematics Continuity and Differentiability Q #870
KNOWLEDGE BASED
APPLY
2 Marks 2023 VSA
If $y=x^{\frac{1}{x}}$ then find $\frac{dy}{dx}$ at $x=1$.

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Step-by-Step Solution

Given: \(y = x^{\frac{1}{x}}\)

Taking the natural logarithm of both sides:

\(\ln y = \ln \left(x^{\frac{1}{x}}\right)\)

\(\ln y = \frac{1}{x} \ln x\)

Differentiating both sides with respect to \(x\):

\(\frac{1}{y} \frac{dy}{dx} = \frac{d}{dx} \left(\frac{1}{x} \ln x\right)\)

Using the product rule:

\(\frac{1}{y} \frac{dy}{dx} = \left(-\frac{1}{x^2}\right) \ln x + \frac{1}{x} \left(\frac{1}{x}\right)\)

\(\frac{1}{y} \frac{dy}{dx} = -\frac{\ln x}{x^2} + \frac{1}{x^2}\)

\(\frac{1}{y} \frac{dy}{dx} = \frac{1 - \ln x}{x^2}\)

Now, solve for \(\frac{dy}{dx}\):

\(\frac{dy}{dx} = y \left(\frac{1 - \ln x}{x^2}\right)\)

\(\frac{dy}{dx} = x^{\frac{1}{x}} \left(\frac{1 - \ln x}{x^2}\right)\)

Evaluate \(\frac{dy}{dx}\) at \(x = 1\):

\(\left.\frac{dy}{dx}\right|_{x=1} = (1)^{\frac{1}{1}} \left(\frac{1 - \ln 1}{1^2}\right)\)

\(\left.\frac{dy}{dx}\right|_{x=1} = 1 \left(\frac{1 - 0}{1}\right)\)

\(\left.\frac{dy}{dx}\right|_{x=1} = 1\)

Correct Answer: 1

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student needs to apply the concepts of differentiation and logarithmic differentiation to find the derivative and then evaluate it at a specific point.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to follow a specific procedure to solve the problem, including logarithmic differentiation and substitution.
Syllabus Audit: In the context of CBSE Class 12, this is classified as KNOWLEDGE. The question directly tests the student's knowledge of differentiation techniques taught in the textbook.