CBSE Class 12 Mathematics Differential Equations Q #1790
COMPETENCY BASED
APPLY
3 Marks 2026 AISSCE(Board Exam) SA
Find the general solution of the differential equation $2x^{2}\frac{dy}{dx}=y^{2}+2xy.$

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Detailed Solution

Step 1: Identify the type of differential equation

The given equation is $2x^{2}\frac{dy}{dx} = y^{2} + 2xy$. Rearranging it, we get $\frac{dy}{dx} = \frac{y^{2} + 2xy}{2x^{2}}$. Since the numerator and denominator are homogeneous functions of degree 2, this is a homogeneous differential equation.

Step 2: Substitution

Let $y = vx$. Then, differentiating with respect to $x$, we get $\frac{dy}{dx} = v + x\frac{dv}{dx}$. Substituting these into the equation:

$$v + x\frac{dv}{dx} = \frac{(vx)^{2} + 2x(vx)}{2x^{2}}$$ $$v + x\frac{dv}{dx} = \frac{v^{2} + 2v}{2}$$

Step 3: Separate variables

Subtract $v$ from both sides:

$$x\frac{dv}{dx} = \frac{v^{2} + 2v - 2v}{2} = \frac{v^{2}}{2}$$ $$\frac{2}{v^{2}} dv = \frac{1}{x} dx$$

Step 4: Integrate and substitute back

Integrating both sides:

$$\int 2v^{-2} dv = \int \frac{1}{x} dx$$ $$-2v^{-1} = \ln|x| + C$$ $$-\frac{2}{v} = \ln|x| + C$$ Since $v = \frac{y}{x}$, we have $-\frac{2x}{y} = \ln|x| + C$, or $y = \frac{-2x}{\ln|x| + C}$.

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

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student must identify the homogeneous nature of the equation and apply the standard substitution method to transform it into a separable variable form.
Knowledge Dimension: PROCEDURAL
Justification: The problem requires a specific sequence of algorithmic steps (substitution, simplification, integration) to reach the solution.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. This aligns with the Differential Equations chapter, testing the student's ability to solve homogeneous equations, a core competency in the Calculus unit.