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Please solve RD Sharma Class 12 Chapter 21 Differential Equation Exercise Multiple Choice Question Question 28 maths textbook solution.

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Answer : \text { (d) } x^{3}+y^{3}=12 x+C

Hint: Use Variable separable form i.e. separate y and x terms by taking x terms to one side and y terms to the other.

Given:   x^{2}+y^{2} \frac{d y}{d x}=4

Explanation : y^{2} \frac{d y}{d x}=4-x^{2}

\Rightarrow y^{2} d y=d x\left(4-x^{2}\right)

Integrate both sides

\begin{aligned} &\Rightarrow \frac{y^{3}}{3}=4 x-\frac{x^{3}}{3}+C_{1} \\ &\Rightarrow y^{3}=3(4 x)-3\left(\frac{x^{3}}{3}\right)+3 C_{1} \end{aligned}

\begin{aligned} &\Rightarrow y^{3}=12 x-x^{3}+3 C_{1} \\ &\Rightarrow x^{3}+y^{3}=12 x+3 C_{1} \\ &\Rightarrow x^{3}+y^{3}=12 x+C\; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \quad\left[C=3 C_{1}\right] \end{aligned}

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