7t Two solutions to y''+ 11y' + 28y = 0 are yi = e , 42 = e-4t. a) Find the Wronskian. W = b) Find the solution satisfying the initial conditions y(0) = 0, y'(0) = - 18
7t Two solutions to y''+ 11y' + 28y = 0 are yi = e , 42 = e-4t. a) Find the Wronskian. W = b) Find the solution satisfying the initial conditions y(0) = 0, y'(0) = - 18
Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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![**Differential Equations - Problem Solving**
**Problem Statement:**
Two solutions to the differential equation \( y'' + 11y' + 28y = 0 \) are \( y_1 = e^{-7t} \) and \( y_2 = e^{-4t} \).
a) Find the Wronskian.
\[ W = \_\_\_\_\_\_ \]
b) Find the solution that satisfies the initial conditions \( y(0) = 0 \), \( y'(0) = -18 \).
\[ y = \_\_\_\_\_\_ \]
---
**Solution Approach:**
1. **Wronskian Calculation:**
The Wronskian \( W \) of two solutions \( y_1(t) \) and \( y_2(t) \) is given by:
\[ W = y_1(t) y_2'(t) - y_2(t) y_1'(t). \]
- For \( y_1(t) = e^{-7t} \):
\[ y_1'(t) = -7e^{-7t}. \]
- For \( y_2(t) = e^{-4t} \):
\[ y_2'(t) = -4e^{-4t}. \]
Substituting into the Wronskian formula:
\[ W = e^{-7t} (-4e^{-4t}) - e^{-4t} (-7e^{-7t}). \]
2. **Finding the Particular Solution:**
We can express the general solution of the differential equation as:
\[ y(t) = C_1 y_1(t) + C_2 y_2(t) = C_1 e^{-7t} + C_2 e^{-4t}. \]
Using the initial conditions \( y(0) = 0 \) and \( y'(0) = -18 \):
- At \( t = 0 \):
\[ y(0) = C_1 e^{0} + C_2 e^{0} = C_1 + C_2 = 0. \]
Therefore, \( C_1 + C_2 = 0 \).
- The derivative of \( y \) is:
\[ y'(t) = -7C](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fc700bc18-61e4-4e04-a31d-52f10b21c2d0%2F7394cf20-af81-4981-8074-7632e7e86733%2Fn44ey0h_processed.jpeg&w=3840&q=75)
Transcribed Image Text:**Differential Equations - Problem Solving**
**Problem Statement:**
Two solutions to the differential equation \( y'' + 11y' + 28y = 0 \) are \( y_1 = e^{-7t} \) and \( y_2 = e^{-4t} \).
a) Find the Wronskian.
\[ W = \_\_\_\_\_\_ \]
b) Find the solution that satisfies the initial conditions \( y(0) = 0 \), \( y'(0) = -18 \).
\[ y = \_\_\_\_\_\_ \]
---
**Solution Approach:**
1. **Wronskian Calculation:**
The Wronskian \( W \) of two solutions \( y_1(t) \) and \( y_2(t) \) is given by:
\[ W = y_1(t) y_2'(t) - y_2(t) y_1'(t). \]
- For \( y_1(t) = e^{-7t} \):
\[ y_1'(t) = -7e^{-7t}. \]
- For \( y_2(t) = e^{-4t} \):
\[ y_2'(t) = -4e^{-4t}. \]
Substituting into the Wronskian formula:
\[ W = e^{-7t} (-4e^{-4t}) - e^{-4t} (-7e^{-7t}). \]
2. **Finding the Particular Solution:**
We can express the general solution of the differential equation as:
\[ y(t) = C_1 y_1(t) + C_2 y_2(t) = C_1 e^{-7t} + C_2 e^{-4t}. \]
Using the initial conditions \( y(0) = 0 \) and \( y'(0) = -18 \):
- At \( t = 0 \):
\[ y(0) = C_1 e^{0} + C_2 e^{0} = C_1 + C_2 = 0. \]
Therefore, \( C_1 + C_2 = 0 \).
- The derivative of \( y \) is:
\[ y'(t) = -7C
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