Class CBSE Class 12 Mathematics Derivatives Q #1289
KNOWLEDGE BASED
UNDERSTAND
2 Marks 2024 AISSCE(Board Exam) VSA
If $y=\sqrt{tan\sqrt{x}}$ , prove that $\sqrt{x}\frac{dy}{dx}=\frac{1+y^{4}}{4y}$

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Detailed Solution

Step 1: Differentiate $y$ with respect to $x$

Given $y = \sqrt{\tan\sqrt{x}}$. We need to find $\frac{dy}{dx}$. Let's differentiate both sides with respect to $x$ using the chain rule. $$\frac{dy}{dx} = \frac{d}{dx} (\sqrt{\tan\sqrt{x}})$$ $$\frac{dy}{dx} = \frac{1}{2\sqrt{\tan\sqrt{x}}} \cdot \frac{d}{dx} (\tan\sqrt{x})$$ $$\frac{dy}{dx} = \frac{1}{2\sqrt{\tan\sqrt{x}}} \cdot \sec^2(\sqrt{x}) \cdot \frac{d}{dx} (\sqrt{x})$$ $$\frac{dy}{dx} = \frac{1}{2\sqrt{\tan\sqrt{x}}} \cdot \sec^2(\sqrt{x}) \cdot \frac{1}{2\sqrt{x}}$$ $$\frac{dy}{dx} = \frac{\sec^2(\sqrt{x})}{4\sqrt{x}\sqrt{\tan\sqrt{x}}}$$ Since $y = \sqrt{\tan\sqrt{x}}$, we can write: $$\frac{dy}{dx} = \frac{\sec^2(\sqrt{x})}{4\sqrt{x}y}$$

Step 2: Isolate $\sqrt{x}\frac{dy}{dx}$

Now, we want to find $\sqrt{x}\frac{dy}{dx}$: $$\sqrt{x}\frac{dy}{dx} = \sqrt{x} \cdot \frac{\sec^2(\sqrt{x})}{4\sqrt{x}y}$$ $$\sqrt{x}\frac{dy}{dx} = \frac{\sec^2(\sqrt{x})}{4y}$$

Step 3: Express $\sec^2(\sqrt{x})$ in terms of $y$

We know that $\sec^2(\sqrt{x}) = 1 + \tan^2(\sqrt{x})$. Also, $y = \sqrt{\tan\sqrt{x}}$, so $y^2 = \tan\sqrt{x}$ and $y^4 = \tan^2\sqrt{x}$. Therefore, $\sec^2(\sqrt{x}) = 1 + y^4$. Substituting this into the equation for $\sqrt{x}\frac{dy}{dx}$: $$\sqrt{x}\frac{dy}{dx} = \frac{1 + y^4}{4y}$$

Final Answer: $\sqrt{x}\frac{dy}{dx} = \frac{1+y^{4}}{4y}$

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Pedagogical Audit
Bloom's Analysis: This is an UNDERSTAND question because the student needs to understand the chain rule of differentiation and trigonometric identities to manipulate the given expression and arrive at the required result.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to apply the chain rule of differentiation and trigonometric identities, which are procedural knowledge.
Syllabus Audit: In the context of CBSE Class 12, this is classified as KNOWLEDGE. The question directly tests the student's knowledge of differentiation rules and trigonometric identities as covered in the textbook.