Find the Laplace transform L{f(t)} where f(t) = { sint, 0≤t

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
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## Laplace Transform of a Piecewise Function

In this example, we are asked to find the Laplace transform \(\mathcal{L}\{f(t)\}\) of the function \( f(t) \) defined as:

\[ 
f(t) = \begin{cases} 
\sin(t), & 0 \le t < \pi \\
0, & t \ge \pi 
\end{cases}
\]

### Step-by-Step Solution:

The Laplace transform of a function \( f(t) \) is given by the integral:

\[ \mathcal{L}\{f(t)\} = \int_0^\infty f(t)e^{-st} \, dt \]

Where \( s \) is a complex number such that the integral converges.

### Given Function Breakdown

1. For \( 0 \le t < \pi \), \( f(t) = \sin(t) \).
2. For \( t \ge \pi \), \( f(t) = 0 \).

### Applying the Laplace Transform to Each Interval

**Interval 1: \( 0 \le t < \pi \)**

\[ 
\begin{aligned}
&\mathcal{L}\{f(t)\text{ on } [0,\pi)\} = \int_0^\pi \sin(t)e^{-st} \, dt
\end{aligned}
\]

**Interval 2: \( t \ge \pi \)**

Since \( f(t) = 0 \) for \( t \ge \pi \),

\[ 
\begin{aligned}
&\mathcal{L}\{f(t)\text{ on } [\pi,\infty)\} = \int_\pi^\infty 0 \cdot e^{-st} \, dt  = 0 
\end{aligned}
\]

Combining both intervals, we integrate only on \( 0 \leq t < \pi \):

\[ 
\begin{aligned}
\mathcal{L}\{f(t)\} &= \int_0^\pi \sin(t)e^{-st} \, dt
\end{aligned}
\]

### Evaluating the Integral

To solve \( \int_0^\pi \sin(t)e^{-st} dt \), we use integration by parts or recognize it as a standard Laplace transform of \( \sin(t) \) multiplied
Transcribed Image Text:## Laplace Transform of a Piecewise Function In this example, we are asked to find the Laplace transform \(\mathcal{L}\{f(t)\}\) of the function \( f(t) \) defined as: \[ f(t) = \begin{cases} \sin(t), & 0 \le t < \pi \\ 0, & t \ge \pi \end{cases} \] ### Step-by-Step Solution: The Laplace transform of a function \( f(t) \) is given by the integral: \[ \mathcal{L}\{f(t)\} = \int_0^\infty f(t)e^{-st} \, dt \] Where \( s \) is a complex number such that the integral converges. ### Given Function Breakdown 1. For \( 0 \le t < \pi \), \( f(t) = \sin(t) \). 2. For \( t \ge \pi \), \( f(t) = 0 \). ### Applying the Laplace Transform to Each Interval **Interval 1: \( 0 \le t < \pi \)** \[ \begin{aligned} &\mathcal{L}\{f(t)\text{ on } [0,\pi)\} = \int_0^\pi \sin(t)e^{-st} \, dt \end{aligned} \] **Interval 2: \( t \ge \pi \)** Since \( f(t) = 0 \) for \( t \ge \pi \), \[ \begin{aligned} &\mathcal{L}\{f(t)\text{ on } [\pi,\infty)\} = \int_\pi^\infty 0 \cdot e^{-st} \, dt = 0 \end{aligned} \] Combining both intervals, we integrate only on \( 0 \leq t < \pi \): \[ \begin{aligned} \mathcal{L}\{f(t)\} &= \int_0^\pi \sin(t)e^{-st} \, dt \end{aligned} \] ### Evaluating the Integral To solve \( \int_0^\pi \sin(t)e^{-st} dt \), we use integration by parts or recognize it as a standard Laplace transform of \( \sin(t) \) multiplied
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