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Solution of the differential equation ...

Solution of the differential equation
`x(dy)/(dx) +y log y=xy e^(x)` is
`x log y = e^(x) (x-1) +c`,

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To solve the differential equation \( x \frac{dy}{dx} + y \log y = xy e^x \), we will follow these steps: ### Step 1: Rewrite the equation First, we can rewrite the given differential equation in a more manageable form. We divide the entire equation by \( xy \): \[ \frac{1}{y} \frac{dy}{dx} + \frac{\log y}{x} = e^x \] ### Step 2: Substitution Next, we can use a substitution to simplify the equation. Let \( v = \log y \). Then, we have: \[ y = e^v \quad \text{and} \quad \frac{dy}{dx} = e^v \frac{dv}{dx} \] Substituting these into the equation gives: \[ \frac{1}{e^v} e^v \frac{dv}{dx} + \frac{v}{x} = e^x \] This simplifies to: \[ \frac{dv}{dx} + \frac{v}{x} = e^x \] ### Step 3: Identify the linear differential equation The equation \( \frac{dv}{dx} + \frac{v}{x} = e^x \) is a linear differential equation in the standard form: \[ \frac{dv}{dx} + P(x)v = Q(x) \] where \( P(x) = \frac{1}{x} \) and \( Q(x) = e^x \). ### Step 4: Find the integrating factor The integrating factor \( \mu(x) \) is given by: \[ \mu(x) = e^{\int P(x) \, dx} = e^{\int \frac{1}{x} \, dx} = e^{\log x} = x \] ### Step 5: Multiply through by the integrating factor We multiply the entire differential equation by the integrating factor \( x \): \[ x \frac{dv}{dx} + v = x e^x \] ### Step 6: Solve the equation The left-hand side can be rewritten as the derivative of a product: \[ \frac{d}{dx}(xv) = x e^x \] Integrating both sides gives: \[ xv = \int x e^x \, dx \] To solve the integral on the right, we use integration by parts: Let \( u = x \) and \( dv = e^x \, dx \). Then \( du = dx \) and \( v = e^x \). Using integration by parts: \[ \int x e^x \, dx = x e^x - \int e^x \, dx = x e^x - e^x + C \] Thus, we have: \[ xv = x e^x - e^x + C \] ### Step 7: Solve for \( v \) Now, we solve for \( v \): \[ v = e^x - \frac{e^x}{x} + \frac{C}{x} \] Recalling that \( v = \log y \), we substitute back: \[ \log y = e^x - \frac{e^x}{x} + \frac{C}{x} \] ### Step 8: Exponentiate to find \( y \) Exponentiating both sides gives: \[ y = e^{e^x - \frac{e^x}{x} + \frac{C}{x}} = e^{e^x} \cdot e^{-\frac{e^x}{x}} \cdot e^{\frac{C}{x}} \] ### Final Step: Rearranging the solution We can rearrange the solution to match the form given in the question: \[ x \log y = e^x (x - 1) + C \] ### Conclusion Thus, we have shown that the solution of the differential equation is indeed: \[ x \log y = e^x (x - 1) + C \]
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