CBSE Class 12 Mathematics Differential Equations Q #1792
COMPETENCY BASED
APPLY
3 Marks 2026 AISSCE(Board Exam) SA
Solve the differential equation $(x+2y^{3})dy=y~dx$.

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Detailed Solution

Step 1: Rearrange the equation

Given the differential equation: $$(x + 2y^3) dy = y dx$$ Divide both sides by $dy$ and $y$ to express it in the form $\frac{dx}{dy} + P(y)x = Q(y)$: $$\frac{dx}{dy} = \frac{x + 2y^3}{y}$$ $$\frac{dx}{dy} = \frac{x}{y} + 2y^2$$ $$\frac{dx}{dy} - \frac{1}{y}x = 2y^2$$

Step 2: Identify the Integrating Factor (IF)

This is a linear differential equation of the form $\frac{dx}{dy} + P(y)x = Q(y)$, where $P(y) = -\frac{1}{y}$ and $Q(y) = 2y^2$. The Integrating Factor is given by: $$IF = e^{\int P(y) dy} = e^{\int -\frac{1}{y} dy} = e^{-\ln|y|} = e^{\ln|y^{-1}|} = \frac{1}{y}$$

Step 3: Solve the equation

The general solution is given by $x \cdot (IF) = \int Q(y) \cdot (IF) dy + C$: $$x \cdot \frac{1}{y} = \int (2y^2) \cdot \frac{1}{y} dy + C$$ $$\frac{x}{y} = \int 2y dy + C$$ $$\frac{x}{y} = y^2 + C$$ $$x = y^3 + Cy$$

Final Answer: x = y^3 + Cy

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student must recognize the standard form of a linear differential equation and apply the integrating factor method to solve it.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the execution of a specific algorithmic process (identifying the form, finding the IF, and integrating) to reach the solution.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. It tests the student's ability to manipulate differential equations into standard forms, a core competency in the Calculus unit.