Question
upstudy study bank question image url

Find the general solution to the differential equation Put the problem in standard form. \( x^{2}-3 x y+x \frac{d y}{d x}=0 \) Find the integrating factor, \( \rho(x)= \) Find \( y(x)= \) Use \( C \) as the unknown constant.

Ask by John Floyd. in the United States
Mar 20,2025

Upstudy AI Solution

Tutor-Verified Answer

Answer

The general solution to the differential equation is \( y(x) = \frac{x}{3} + \frac{1}{9} + C e^{3x} \), where \( C \) is the constant of integration.

Solution

We start with the differential equation \[ x^{2} - 3xy + x\frac{dy}{dx} = 0. \] **Step 1. Put the equation in standard form** Since \(x \neq 0\), we can divide the entire equation by \(x\): \[ \frac{x^{2}}{x} - 3y + \frac{dy}{dx} = 0 \quad \Longrightarrow \quad x - 3y + \frac{dy}{dx} = 0. \] Rearrange to isolate \(\frac{dy}{dx}\): \[ \frac{dy}{dx} = 3y - x. \] Write this in standard linear form: \[ \frac{dy}{dx} - 3y = -x. \] Here, the coefficient function (in the standard linear form \(\frac{dy}{dx} + p(x)y = q(x)\)) is \[ p(x) = -3. \] --- **Step 2. Find the integrating factor, \(\rho(x)\)** The integrating factor is given by \[ \rho(x)= e^{\int p(x) \, dx} = e^{\int -3 \, dx} = e^{-3x}. \] Thus, \[ \rho(x) = e^{-3x}. \] --- **Step 3. Solve the differential equation** Multiply the standard form by the integrating factor: \[ e^{-3x}\frac{dy}{dx} - 3e^{-3x}y = -x e^{-3x}. \] Notice that the left-hand side is the derivative of \(\left(e^{-3x}y\right)\): \[ \frac{d}{dx}\left(e^{-3x}y\right) = -x e^{-3x}. \] Now integrate both sides with respect to \(x\): \[ \int \frac{d}{dx}\left(e^{-3x}y\right) \, dx = \int -x e^{-3x} \, dx. \] This gives \[ e^{-3x}y = \int -x e^{-3x} \, dx. \] **Step 3a. Evaluate the integral \(\int -x e^{-3x} \, dx\)** Let \[ I = \int -x e^{-3x} \, dx. \] Use integration by parts where \[ u = -x, \quad dv = e^{-3x}dx. \] Then \[ du = -dx, \quad v = \int e^{-3x}dx = -\frac{1}{3}e^{-3x}. \] Now, applying integration by parts: \[ I = u v - \int v\,du = \left(-x\right)\left(-\frac{1}{3}e^{-3x}\right) - \int \left(-\frac{1}{3}e^{-3x}\right)(-dx). \] Simplify the terms: \[ I = \frac{x}{3}e^{-3x} - \int \frac{1}{3}e^{-3x}\,dx. \] Now, integrate the remaining integral: \[ \int e^{-3x}\,dx = -\frac{1}{3}e^{-3x}. \] Thus, \[ I = \frac{x}{3}e^{-3x} - \frac{1}{3}\left(-\frac{1}{3}e^{-3x}\right) = \frac{x}{3}e^{-3x} + \frac{1}{9}e^{-3x}. \] So we have \[ e^{-3x}y = e^{-3x}\left(\frac{x}{3} + \frac{1}{9}\right) + C, \] where \(C\) is the constant of integration. --- **Step 4. Solve for \(y\)** Multiply both sides of the equation by \(e^{3x}\) to solve for \(y\): \[ y = \frac{x}{3} + \frac{1}{9} + C e^{3x}. \] --- **Final Answers** 1. The standard form of the differential equation is \[ \frac{dy}{dx} - 3y = -x. \] 2. The integrating factor is \[ \rho(x)= e^{-3x}. \] 3. The general solution is \[ y(x)= \frac{x}{3} + \frac{1}{9} + C e^{3x}. \]

Answered by UpStudy AI and reviewed by a Professional Tutor

error msg
Explain
Simplify this solution

Bonus Knowledge

To put the differential equation in standard form, we will first rearrange it. Start with: \[ x^2 - 3xy + x \frac{dy}{dx} = 0 \] This can be rewritten as: \[ x \frac{dy}{dx} = 3xy - x^2 \] Now, divide through by \( x \) (assuming \( x \neq 0 \)): \[ \frac{dy}{dx} = 3y - x \] Next, we have the first-order linear differential equation in standard form: \[ \frac{dy}{dx} - 3y = -x \] To find the integrating factor, \( \rho(x) \), we use the formula: \[ \rho(x) = e^{\int -3 \, dx} = e^{-3x} \] Now, multiplying both sides of the equation by the integrating factor: \[ e^{-3x} \frac{dy}{dx} - 3e^{-3x}y = -xe^{-3x} \] The left-hand side can be recognized as the derivative of \( e^{-3x}y \): \[ \frac{d}{dx}(e^{-3x}y) = -xe^{-3x} \] Integrating both sides with respect to \( x \): \[ e^{-3x}y = \int -xe^{-3x} \, dx \] This integral can be tackled using integration by parts. Let \( u = x \) and \( dv = e^{-3x}dx \): Then \( du = dx \) and \( v = -\frac{1}{3}e^{-3x} \). Applying integration by parts: \[ \int -xe^{-3x} \, dx = -\frac{x}{3}e^{-3x} - \int -\frac{1}{3}e^{-3x} \, dx \] \[ = -\frac{x}{3}e^{-3x} + \frac{1}{9}e^{-3x} + C \] Thus: \[ e^{-3x}y = -\frac{x}{3}e^{-3x} + \frac{1}{9}e^{-3x} + C \] Now multiplying through by \( e^{3x} \): \[ y = -\frac{x}{3} + \frac{1}{9} + Ce^{3x} \] So the general solution for \( y(x) \) is: \[ y(x) = -\frac{x}{3} + \frac{1}{9} + Ce^{3x} \] Teamwork makes the dream work! Get ready to solve some diff equations! For those intrigued about how history and real-life connect with differential equations, you're in for a treat!

Latest Calculus Questions

Try Premium now!
Try Premium and ask Thoth AI unlimited math questions now!
Maybe later Go Premium
Study can be a real struggle
Why not UpStudy it?
Select your plan below
Premium

You can enjoy

Start now
  • Step-by-step explanations
  • 24/7 expert live tutors
  • Unlimited number of questions
  • No interruptions
  • Full access to Answer and Solution
  • Full Access to PDF Chat, UpStudy Chat, Browsing Chat
Basic

Totally free but limited

  • Limited Solution
Welcome to UpStudy!
Please sign in to continue the Thoth AI Chat journey
Continue with Email
Or continue with
By clicking “Sign in”, you agree to our Terms of Use & Privacy Policy