For $y ≠ 0$, the particular solution of the differential equation $2ye^{x/y} dx + (y - 2xe^{x/y})dy = 0$ at the point (1, 1) is |
$ln |y|+ 2(e^{x/y}-e) = 0$ $ln |y|- 2(e^{x/y}-e) = 0$ $ln |y|+\frac{1}{2}(e^{x/y}-e) = 0$ $ln |y|-\frac{1}{2}(e^{x/y}-e) = 0$ |
$ln |y|+ 2(e^{x/y}-e) = 0$ |
The correct answer is Option (1) → $ln |y|+ 2(e^{x/y}-e) = 0$ Given differential equation: $2y e^{\frac{x}{y}} dx + \left(y - 2x e^{\frac{x}{y}}\right) dy = 0$ Rewriting: $2y e^{\frac{x}{y}} \, dx + \left(y - 2x e^{\frac{x}{y}}\right) \, dy = 0$ Divide the whole equation by $y$ (since $y \ne 0$): $2 e^{\frac{x}{y}} \, dx + \left(1 - \frac{2x}{y} e^{\frac{x}{y}}\right) \, dy = 0$ Let $u = \frac{x}{y} \Rightarrow x = uy$ Differentiate: $dx = u \, dy + y \, du$ Substitute into the original equation: $2 e^{u}(u \, dy + y \, du) + \left(1 - 2u e^{u} \right) dy = 0$ Distribute: $2u e^u \, dy + 2y e^u \, du + \left(1 - 2u e^u \right) dy = 0$ Combine $dy$ terms: $\left(2u e^u + 1 - 2u e^u\right) dy + 2y e^u \, du = 0$ $dy + 2y e^u \, du = 0$ $\Rightarrow dy = -2y e^u \, du$ Separate variables: $\frac{dy}{y} = -2 e^u \, du$ Integrate both sides: $\int \frac{1}{y} dy = -2 \int e^u \, du$ $\ln |y| = -2 e^u + C$ Recall $u = \frac{x}{y}$: $\ln |y| = -2 e^{\frac{x}{y}} + C$ Use point $(1, 1)$ to find $C$: $\ln 1 = -2 e^{1} + C \Rightarrow 0 = -2e + C \Rightarrow C = 2e$ Final answer: ${\ln y = -2 e^{\frac{x}{y}} + 2e}$ |