y' - ycosx = cos x

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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**Understanding First-Order Linear Differential Equations**

On this educational page, we discuss first-order linear differential equations. The differential equation presented here is:

\[ y' - y \cos x = \cos x \]

### Explanation of Terms:
- \( y' \) denotes the first derivative of \( y \) with respect to \( x \).
- \( \cos x \) is the cosine function, which is a trigonometric function of \( x \).

### Structure of the Equation:
This equation is of the form:

\[ y' + P(x)y = Q(x) \]

where:
- \( P(x) = -\cos x \)
- \( Q(x) = \cos x \)

### Steps to Solve the Equation:
1. **Identify** \( P(x) \) and \( Q(x) \).
2. **Find the integrating factor** \( \mu(x) \), which is given by:
   
   \[ \mu(x) = e^{\int P(x) \, dx} \]

3. **Multiply** the whole differential equation by \( \mu(x) \) to facilitate finding the solution.

### Detailed Steps:
1. For our equation:

   \[ P(x) = -\cos x \]

2. The integral of \( P(x) \):

   \[ \int -\cos x \, dx = -\sin x \]

3. The integrating factor:

   \[ \mu(x) = e^{-\sin x} \]

4. Multiplying the original equation by \( \mu(x) \):

   \[ e^{-\sin x} y' - e^{-\sin x} y \cos x = e^{-\sin x} \cos x \]

   which simplifies the integration process.

### Final Step:
After finding the integrating factor, you integrate both sides with respect to \( x \) to find the general solution for \( y \).

### Additional Notes:
For visual learners, it may be beneficial to graph the functions involved using graphing software or tools. Understanding how \( \cos x \) behaves helps intuitively grasp how \( y \) changes with respect to \( x \).

Feel free to experiment by solving similar differential equations to solidify your understanding!
Transcribed Image Text:**Understanding First-Order Linear Differential Equations** On this educational page, we discuss first-order linear differential equations. The differential equation presented here is: \[ y' - y \cos x = \cos x \] ### Explanation of Terms: - \( y' \) denotes the first derivative of \( y \) with respect to \( x \). - \( \cos x \) is the cosine function, which is a trigonometric function of \( x \). ### Structure of the Equation: This equation is of the form: \[ y' + P(x)y = Q(x) \] where: - \( P(x) = -\cos x \) - \( Q(x) = \cos x \) ### Steps to Solve the Equation: 1. **Identify** \( P(x) \) and \( Q(x) \). 2. **Find the integrating factor** \( \mu(x) \), which is given by: \[ \mu(x) = e^{\int P(x) \, dx} \] 3. **Multiply** the whole differential equation by \( \mu(x) \) to facilitate finding the solution. ### Detailed Steps: 1. For our equation: \[ P(x) = -\cos x \] 2. The integral of \( P(x) \): \[ \int -\cos x \, dx = -\sin x \] 3. The integrating factor: \[ \mu(x) = e^{-\sin x} \] 4. Multiplying the original equation by \( \mu(x) \): \[ e^{-\sin x} y' - e^{-\sin x} y \cos x = e^{-\sin x} \cos x \] which simplifies the integration process. ### Final Step: After finding the integrating factor, you integrate both sides with respect to \( x \) to find the general solution for \( y \). ### Additional Notes: For visual learners, it may be beneficial to graph the functions involved using graphing software or tools. Understanding how \( \cos x \) behaves helps intuitively grasp how \( y \) changes with respect to \( x \). Feel free to experiment by solving similar differential equations to solidify your understanding!
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