4y" + (y') = 0

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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Differential equations
### Differential Equation Problem

**Solve completely:**

\[4y'' + (y')^3 = 0\]

**Solution Steps:**

1. **Identify the Type of Equation:**
   - This is a second-order differential equation where \( y'' \) represents the second derivative of \( y \) with respect to \( x \), and \( y' \) represents the first derivative of \( y \).

2. **Transformation to a Simpler Form:**
   - To solve this, let's use \( v = y' \), where \( v \) is a function of \( y \). Then \( y'' = v \frac{dv}{dy} \).
   - Substitute these into the given equation:
     \[
     4v \frac{dv}{dy} + v^3 = 0
     \]

3. **Separation of Variables:**
   - Factor out common terms and separate variables:
     \[
     v (4 \frac{dv}{dy} + v^2) = 0
     \]
     \[
     v = 0 \quad \text{or} \quad 4 \frac{dv}{dy} = -v^2
     \]

4. **Solving for \( v \):**
   - If \( v = 0 \), \( y' = 0 \Rightarrow y = C_1 \).
   - Otherwise:
     \[
     4 \frac{dv}{dy} = -v^2
     \]
     \[
     \frac{4}{v^2} dv = -dy
     \]

5. **Integrate Both Sides:**
   - For the non-trivial solution:
     \[
     \int \frac{4}{v^2} dv = -\int dy
     \]
     \[
     -\frac{4}{v} = y + C_2 \quad \Rightarrow \quad v = -\frac{4}{y + C_2}
     \]

6. **Backward Transformation:**
   - Substitute back \( v = y' \):
     \[
     y' = -\frac{4}{y + C_2}
     \]
   - Separate variables again for integration:
     \[
     (y + C_2) dy = -4 dx
     \]
     \[
     \int (y
Transcribed Image Text:### Differential Equation Problem **Solve completely:** \[4y'' + (y')^3 = 0\] **Solution Steps:** 1. **Identify the Type of Equation:** - This is a second-order differential equation where \( y'' \) represents the second derivative of \( y \) with respect to \( x \), and \( y' \) represents the first derivative of \( y \). 2. **Transformation to a Simpler Form:** - To solve this, let's use \( v = y' \), where \( v \) is a function of \( y \). Then \( y'' = v \frac{dv}{dy} \). - Substitute these into the given equation: \[ 4v \frac{dv}{dy} + v^3 = 0 \] 3. **Separation of Variables:** - Factor out common terms and separate variables: \[ v (4 \frac{dv}{dy} + v^2) = 0 \] \[ v = 0 \quad \text{or} \quad 4 \frac{dv}{dy} = -v^2 \] 4. **Solving for \( v \):** - If \( v = 0 \), \( y' = 0 \Rightarrow y = C_1 \). - Otherwise: \[ 4 \frac{dv}{dy} = -v^2 \] \[ \frac{4}{v^2} dv = -dy \] 5. **Integrate Both Sides:** - For the non-trivial solution: \[ \int \frac{4}{v^2} dv = -\int dy \] \[ -\frac{4}{v} = y + C_2 \quad \Rightarrow \quad v = -\frac{4}{y + C_2} \] 6. **Backward Transformation:** - Substitute back \( v = y' \): \[ y' = -\frac{4}{y + C_2} \] - Separate variables again for integration: \[ (y + C_2) dy = -4 dx \] \[ \int (y
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