Solve the differential equation by variation of parameters. 9x y(x) = y" - 9y = C₁e³r 3x 3x -3.x + C₂e -3.x + e (- 4 - 3r²) X

Advanced Engineering Mathematics
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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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## Solving Differential Equations by Variation of Parameters

In this section, we will explore the method of solving a second-order linear differential equation using the variation of parameters. The differential equation given is:

\[ y'' - 9y = \frac{9x}{e^{3x}} \]

### Steps to Solve by Variation of Parameters

1. **Identify the Homogeneous Part**: 
   - The associated homogeneous equation is:
     \[ y'' - 9y = 0 \]

2. **Solve the Homogeneous Equation**:
   - The solution to the homogeneous equation can be found by solving the characteristic equation:
     \[ r^2 - 9 = 0 \]
     \[ r = \pm 3 \]
   - Therefore, the general solution to the homogeneous equation is:
     \[ y_h(x) = C_1 e^{3x} + C_2 e^{-3x} \]

3. **Particular Solution by Variation of Parameters**:
   - Assume a particular solution of the form:
     \[ y_p(x) = u_1(x) e^{3x} + u_2(x) e^{-3x} \]
   - Use the method of variation of parameters to find \( u_1(x) \) and \( u_2(x) \).

4. **Construct the General Solution**:
   - Combine the homogeneous solution and the particular solution to express the complete solution:
     \[ y(x) = y_h(x) + y_p(x) \]

The general solution to the differential equation given is:

\[ y(x) = C_1 e^{3x} + C_2 e^{-3x} + e^{-3x} \left( -\frac{1}{4} - 3x^2 \right) \]

Where \( C_1 \) and \( C_2 \) are constants determined by initial conditions.

Note: The final expression inside the box represents the complete solution, highlighting both the homogeneous and particular solutions combined.

By solving step by step, students will gain a better understanding of applying variation of parameters and solving non-homogeneous differential equations.
Transcribed Image Text:## Solving Differential Equations by Variation of Parameters In this section, we will explore the method of solving a second-order linear differential equation using the variation of parameters. The differential equation given is: \[ y'' - 9y = \frac{9x}{e^{3x}} \] ### Steps to Solve by Variation of Parameters 1. **Identify the Homogeneous Part**: - The associated homogeneous equation is: \[ y'' - 9y = 0 \] 2. **Solve the Homogeneous Equation**: - The solution to the homogeneous equation can be found by solving the characteristic equation: \[ r^2 - 9 = 0 \] \[ r = \pm 3 \] - Therefore, the general solution to the homogeneous equation is: \[ y_h(x) = C_1 e^{3x} + C_2 e^{-3x} \] 3. **Particular Solution by Variation of Parameters**: - Assume a particular solution of the form: \[ y_p(x) = u_1(x) e^{3x} + u_2(x) e^{-3x} \] - Use the method of variation of parameters to find \( u_1(x) \) and \( u_2(x) \). 4. **Construct the General Solution**: - Combine the homogeneous solution and the particular solution to express the complete solution: \[ y(x) = y_h(x) + y_p(x) \] The general solution to the differential equation given is: \[ y(x) = C_1 e^{3x} + C_2 e^{-3x} + e^{-3x} \left( -\frac{1}{4} - 3x^2 \right) \] Where \( C_1 \) and \( C_2 \) are constants determined by initial conditions. Note: The final expression inside the box represents the complete solution, highlighting both the homogeneous and particular solutions combined. By solving step by step, students will gain a better understanding of applying variation of parameters and solving non-homogeneous differential equations.
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