8. Solve the Cauchy-Euler equation 4x²y" + 8xy' + y = 0.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
Question
### Problem 8: Cauchy-Euler Equation

**Objective:** Solve the Cauchy-Euler equation

\[ 4x^2y'' + 8xy' + y = 0. \]

### Explanation

The Cauchy-Euler equation is a type of linear differential equation of the form:

\[ a_n x^n y^{(n)} + a_{n-1} x^{n-1} y^{(n-1)} + \cdots + a_1 x y' + a_0 y = 0. \]

This particular problem provides a second-order Cauchy-Euler equation:

- **\( x^2 \) Coefficient: \( 4x^2 y'' \)**
  - The second derivative \( y'' \) is multiplied by \( 4x^2 \).
  
- **\( x \) Coefficient: \( 8x y' \)**
  - The first derivative \( y' \) is multiplied by \( 8x \).

- **Constant Term: \( y \)**
  - The function \( y \) itself is included as is.

### Method of Solution

1. **Substitution:** Assume a solution of the form \( y = x^m \).
2. **Derivatives:** Compute the first and second derivatives:
   - \( y' = mx^{m-1} \)
   - \( y'' = m(m-1)x^{m-2} \)

3. **Substitute into the Original Equation:** 

   Replace \( y \), \( y' \), and \( y'' \) in the equation with the expressions derived:
   \[
   4x^2(m(m-1)x^{m-2}) + 8x(mx^{m-1}) + x^m = 0.
   \]

4. **Simplify and Solve for \( m \):**

   - Simplifies to: 
   \[
   4m(m-1)x^m + 8mx^m + x^m = 0.
   \]
   - Factor out \( x^m \):
   \[
   x^m(4m(m-1) + 8m + 1) = 0.
   \]
   - Solve the characteristic equation:
   \[
   4m^2 + 4m + 1 = 0.
Transcribed Image Text:### Problem 8: Cauchy-Euler Equation **Objective:** Solve the Cauchy-Euler equation \[ 4x^2y'' + 8xy' + y = 0. \] ### Explanation The Cauchy-Euler equation is a type of linear differential equation of the form: \[ a_n x^n y^{(n)} + a_{n-1} x^{n-1} y^{(n-1)} + \cdots + a_1 x y' + a_0 y = 0. \] This particular problem provides a second-order Cauchy-Euler equation: - **\( x^2 \) Coefficient: \( 4x^2 y'' \)** - The second derivative \( y'' \) is multiplied by \( 4x^2 \). - **\( x \) Coefficient: \( 8x y' \)** - The first derivative \( y' \) is multiplied by \( 8x \). - **Constant Term: \( y \)** - The function \( y \) itself is included as is. ### Method of Solution 1. **Substitution:** Assume a solution of the form \( y = x^m \). 2. **Derivatives:** Compute the first and second derivatives: - \( y' = mx^{m-1} \) - \( y'' = m(m-1)x^{m-2} \) 3. **Substitute into the Original Equation:** Replace \( y \), \( y' \), and \( y'' \) in the equation with the expressions derived: \[ 4x^2(m(m-1)x^{m-2}) + 8x(mx^{m-1}) + x^m = 0. \] 4. **Simplify and Solve for \( m \):** - Simplifies to: \[ 4m(m-1)x^m + 8mx^m + x^m = 0. \] - Factor out \( x^m \): \[ x^m(4m(m-1) + 8m + 1) = 0. \] - Solve the characteristic equation: \[ 4m^2 + 4m + 1 = 0.
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