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Please solve RD Sharma class 12 chapter Differential Equations exercise 21.7 question 38 sub question (iii) maths textbook solution

Answers (1)

Answer: y=e^{\frac{x}{y}}+c

Hint: Separate the terms of x and y and then integrate them.

Given: y e^{\frac{x}{y}} d x=\left(x e^{\frac{x}{y}}+y^{2}\right) d y

Solution: y e^{\frac{x}{y}} d x=\left(x e^{\frac{x}{y}}+y^{2}\right) d y

        \frac{d x}{d y}=\frac{x e^{\frac{x}{y}}+y^{2}}{y_{e}^{\frac{x}{y}}}

        x=v y=>\frac{d x}{d y}=v+y \cdot \frac{d v}{d y}

        v+y \cdot \frac{d v}{d y}=\frac{v y \cdot e^{v}+y^{2}}{y e^{v}}

        \begin{aligned} &y \cdot \frac{d v}{d y}=\frac{v y \cdot e^{v}+y^{2}}{y e^{v}}-v \\\\ &y \cdot \frac{d v}{d y}=\frac{v y \cdot e^{v}+y^{2}-v y e^{v}}{y e^{v}} \end{aligned}

        \begin{aligned} &e^{v} d v=\frac{y d y}{y} \\\\ &e^{v} d v=d y \end{aligned}

         Integrating both sides

        \begin{aligned} &\int e^{y} d v=\int 1 d y \\\\ &y=e^{v}+c \end{aligned}

        Put

        \begin{aligned} &v=\frac{x}{y} \\\\ &y=e^{\frac{x}{y}}+c \end{aligned}

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