the following homogeneous DE. Find a fundamental set of solutions for the DE (1). Form the general solution of (1).

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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Consider the following homogeneous DE. Find a fundamental set of solutions for the DE (1). Form the general solution of (1).

### Problem Statement:
Consider the differential equation:

\[ y'' + y' - 2y = 0. \quad \text{(1)} \]

- Find a fundamental set of solutions for the DE (1). Form the general solution of (1).

### Explanation:
In this problem, we are given a second-order linear homogeneous differential equation. The tasks are to:
1. Find a fundamental set of solutions.
2. Form the general solution based on the fundamental set of solutions.

Here's how you can approach this:

1. **Solve the characteristic equation**:
   - The characteristic equation for a second-order DE in the form \( ay'' + by' + cy = 0 \) is \( ar^2 + br + c = 0 \).
   - For the given DE (1): \( y'' + y' - 2y = 0 \), the characteristic equation is \( r^2 + r - 2 = 0 \).

2. **Find the roots of the characteristic equation**:
   - Factoring the quadratic equation \( r^2 + r - 2 = 0 \): \((r - 1)(r + 2) = 0\).
   - The roots are \( r_1 = 1 \) and \( r_2 = -2 \).

3. **Form the fundamental set of solutions**:
   - The solutions corresponding to the roots \( r_1 \) and \( r_2 \) are \( y_1 = e^{r_1 x} \) and \( y_2 = e^{r_2 x} \).
   - Therefore, the fundamental set of solutions is \( \{e^x, e^{-2x}\} \).

4. **Form the general solution**:
   - The general solution of the DE is a linear combination of the fundamental set of solutions:
   - \( y = C_1 e^x + C_2 e^{-2x} \), where \( C_1 \) and \( C_2 \) are arbitrary constants.

This process leads us to the general solution of the given differential equation.
Transcribed Image Text:### Problem Statement: Consider the differential equation: \[ y'' + y' - 2y = 0. \quad \text{(1)} \] - Find a fundamental set of solutions for the DE (1). Form the general solution of (1). ### Explanation: In this problem, we are given a second-order linear homogeneous differential equation. The tasks are to: 1. Find a fundamental set of solutions. 2. Form the general solution based on the fundamental set of solutions. Here's how you can approach this: 1. **Solve the characteristic equation**: - The characteristic equation for a second-order DE in the form \( ay'' + by' + cy = 0 \) is \( ar^2 + br + c = 0 \). - For the given DE (1): \( y'' + y' - 2y = 0 \), the characteristic equation is \( r^2 + r - 2 = 0 \). 2. **Find the roots of the characteristic equation**: - Factoring the quadratic equation \( r^2 + r - 2 = 0 \): \((r - 1)(r + 2) = 0\). - The roots are \( r_1 = 1 \) and \( r_2 = -2 \). 3. **Form the fundamental set of solutions**: - The solutions corresponding to the roots \( r_1 \) and \( r_2 \) are \( y_1 = e^{r_1 x} \) and \( y_2 = e^{r_2 x} \). - Therefore, the fundamental set of solutions is \( \{e^x, e^{-2x}\} \). 4. **Form the general solution**: - The general solution of the DE is a linear combination of the fundamental set of solutions: - \( y = C_1 e^x + C_2 e^{-2x} \), where \( C_1 \) and \( C_2 \) are arbitrary constants. This process leads us to the general solution of the given differential equation.
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