CBSE Class 12 Mathematics Differential Equations Q #1789
COMPETENCY BASED
APPLY
3 Marks 2026 AISSCE(Board Exam) SA
Find the general solution of the differential equation: $y\log y\frac{dx}{dy}+x=\frac{2}{y}$

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Detailed Solution

Step 1: Standardize the Linear Differential Equation

The given equation is $y\log y\frac{dx}{dy}+x=\frac{2}{y}$. Divide the entire equation by $y\log y$ to bring it into the standard form $\frac{dx}{dy} + P(y)x = Q(y)$:

$$\frac{dx}{dy} + \frac{1}{y\log y}x = \frac{2}{y^2\log y}$$

Step 2: Find the Integrating Factor (IF)

Here, $P(y) = \frac{1}{y\log y}$. The integrating factor is given by $IF = e^{\int P(y) dy}$:

$$IF = e^{\int \frac{1}{y\log y} dy} = e^{\log(\log y)} = \log y$$

Step 3: Apply the General Solution Formula

The solution is $x \cdot (IF) = \int Q(y) \cdot (IF) dy + C$:

$$x \log y = \int \frac{2}{y^2\log y} \cdot \log y \, dy = \int \frac{2}{y^2} dy$$

Step 4: Integrate and Simplify

Integrating $\frac{2}{y^2}$ gives $-2y^{-1} + C$:

$$x \log y = -\frac{2}{y} + C$$

Final Answer: x \log y = -\frac{2}{y} + C

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student must identify the specific form of a linear differential equation and apply the standard algorithm for integrating factors to solve it.
Knowledge Dimension: PROCEDURAL
Justification: The problem requires a step-by-step execution of a mathematical procedure (standardizing, finding IF, and integrating) rather than just recalling a definition.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. This question tests the student's ability to manipulate differential equations into standard forms, a core competency in the Calculus unit.