Advanced Engineering Mathematics
Advanced Engineering Mathematics
10th Edition
ISBN: 9780470458365
Author: Erwin Kreyszig
Publisher: Wiley, John & Sons, Incorporated
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**Example 5: Using Theorem 4.8.2**

**Problem:**
Solve the initial-value problem:

\[ y'' + 4y = \sin 2x, \quad y(0) = 1, \quad y'(0) = -2. \]

**Solution:**
We solve two initial-value problems.

First, we solve \( y'' + 4y = 0, \quad y(0) = 1, \quad y'(0) = -2 \). By applying the initial conditions to the general solution \( y(x) = c_1 \cos 2x + c_2 \sin 2x \) of the homogeneous DE, we find that \( c_1 = 1 \) and \( c_2 = -1 \). Therefore, \( y_h(x) = \cos 2x - \sin 2x \).

Next, we solve \( y'' + 4y = \sin 2x, \quad y(0) = 0, \quad y'(0) = 0 \). Since the left-hand side of the differential equation is the same as the DE in Example 4, the Green’s function is the same, namely, \( G(x, t) = \frac{1}{2} \sin 2(x - t) \). With \( f(t) = \sin 2t \) we see from (10) that the solution of this second problem is \( y_p(x) = \frac{1}{2} \int_{0}^{x} \sin 2(x - t) \sin 2t \, dt \).

Finally, in view of (17) in Theorem 4.8.2, the solution of the original IVP is 

\[ y(x) = y_h(x) + y_p(x) = \cos 2x - \sin 2x + \frac{1}{2} \int_{0}^{x} \sin 2(x - t) \sin 2t \, dt. \quad (19) \]

If desired, we can integrate the definite integral in (19) by using the trigonometric identity

\[ \sin A \sin B = \frac{1}{2} [\cos (A - B) - \cos (A + B)] \]

with \( A = 2(x
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Transcribed Image Text:**Example 5: Using Theorem 4.8.2** **Problem:** Solve the initial-value problem: \[ y'' + 4y = \sin 2x, \quad y(0) = 1, \quad y'(0) = -2. \] **Solution:** We solve two initial-value problems. First, we solve \( y'' + 4y = 0, \quad y(0) = 1, \quad y'(0) = -2 \). By applying the initial conditions to the general solution \( y(x) = c_1 \cos 2x + c_2 \sin 2x \) of the homogeneous DE, we find that \( c_1 = 1 \) and \( c_2 = -1 \). Therefore, \( y_h(x) = \cos 2x - \sin 2x \). Next, we solve \( y'' + 4y = \sin 2x, \quad y(0) = 0, \quad y'(0) = 0 \). Since the left-hand side of the differential equation is the same as the DE in Example 4, the Green’s function is the same, namely, \( G(x, t) = \frac{1}{2} \sin 2(x - t) \). With \( f(t) = \sin 2t \) we see from (10) that the solution of this second problem is \( y_p(x) = \frac{1}{2} \int_{0}^{x} \sin 2(x - t) \sin 2t \, dt \). Finally, in view of (17) in Theorem 4.8.2, the solution of the original IVP is \[ y(x) = y_h(x) + y_p(x) = \cos 2x - \sin 2x + \frac{1}{2} \int_{0}^{x} \sin 2(x - t) \sin 2t \, dt. \quad (19) \] If desired, we can integrate the definite integral in (19) by using the trigonometric identity \[ \sin A \sin B = \frac{1}{2} [\cos (A - B) - \cos (A + B)] \] with \( A = 2(x
Proceed as in this example to find a solution of the given initial-value problem.

\[ x^2y'' - 2xy' + 2y = x, \, y(1) = 3, \, y'(1) = -2 \]

\[ y(x) = \text{________} \]

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Transcribed Image Text:Proceed as in this example to find a solution of the given initial-value problem. \[ x^2y'' - 2xy' + 2y = x, \, y(1) = 3, \, y'(1) = -2 \] \[ y(x) = \text{________} \] Need Help? [Read It]
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