Find the inverse Laplace transform of 7s + 3 s > 0 s2 + 17

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
Question
**Problem:**

Find the inverse Laplace transform of

\[ \frac{7s + 3}{s^2 + 17} \]

for \( s > 0 \). 

**Solution:**

To find the inverse Laplace transform, we can separate the expression into two fractions:

\[ \frac{7s}{s^2 + 17} + \frac{3}{s^2 + 17} \]

**Step 1: Inverse Transform of \( \frac{7s}{s^2 + 17} \)**

Recognizing the form \(\frac{s}{s^2 + a^2}\), the inverse Laplace transform is a cosine function:

\[ \mathcal{L}^{-1}\left\{ \frac{s}{s^2 + a^2} \right\} = \cos(at) \]

For our case, \( a^2 = 17 \), hence \( a = \sqrt{17} \). So the inverse Laplace transform of \( \frac{7s}{s^2 + 17} \) is:

\[ 7 \cos(\sqrt{17}t) \]

**Step 2: Inverse Transform of \( \frac{3}{s^2 + 17} \)**

Recognizing the form \(\frac{1}{s^2 + a^2}\), the inverse Laplace transform is a sine function:

\[ \mathcal{L}^{-1}\left\{ \frac{1}{s^2 + a^2} \right\} = \frac{1}{a}\sin(at) \]

Therefore, the inverse Laplace transform of \( \frac{3}{s^2 + 17} \) is:

\[ \frac{3}{\sqrt{17}} \sin(\sqrt{17} t) \]

**Final Solution:**

Combining both parts, the inverse Laplace transform of the original function is:

\[ 7 \cos(\sqrt{17}t) + \frac{3}{\sqrt{17}} \sin(\sqrt{17}t) \]
Transcribed Image Text:**Problem:** Find the inverse Laplace transform of \[ \frac{7s + 3}{s^2 + 17} \] for \( s > 0 \). **Solution:** To find the inverse Laplace transform, we can separate the expression into two fractions: \[ \frac{7s}{s^2 + 17} + \frac{3}{s^2 + 17} \] **Step 1: Inverse Transform of \( \frac{7s}{s^2 + 17} \)** Recognizing the form \(\frac{s}{s^2 + a^2}\), the inverse Laplace transform is a cosine function: \[ \mathcal{L}^{-1}\left\{ \frac{s}{s^2 + a^2} \right\} = \cos(at) \] For our case, \( a^2 = 17 \), hence \( a = \sqrt{17} \). So the inverse Laplace transform of \( \frac{7s}{s^2 + 17} \) is: \[ 7 \cos(\sqrt{17}t) \] **Step 2: Inverse Transform of \( \frac{3}{s^2 + 17} \)** Recognizing the form \(\frac{1}{s^2 + a^2}\), the inverse Laplace transform is a sine function: \[ \mathcal{L}^{-1}\left\{ \frac{1}{s^2 + a^2} \right\} = \frac{1}{a}\sin(at) \] Therefore, the inverse Laplace transform of \( \frac{3}{s^2 + 17} \) is: \[ \frac{3}{\sqrt{17}} \sin(\sqrt{17} t) \] **Final Solution:** Combining both parts, the inverse Laplace transform of the original function is: \[ 7 \cos(\sqrt{17}t) + \frac{3}{\sqrt{17}} \sin(\sqrt{17}t) \]
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