Section 21.2

Properties and Formulas

We don't need to integrate every time. This section builds our "Table of Transforms" using powerful properties.

1

Introduction

Just like differentiation, the Laplace Transform has rules that allow us to combine simple functions to handle complex ones.

2

Linearity

Theorem

Since integration is linear, the Laplace Transform is linear:

This means we can transform term by term.

3

First Translation Theorem

Concept

Multiplying by an exponential in the time domain causes a shift in the s-domain.

This is crucial for solving DEs with exponential forcing or damping.

Interactive: Shifting S

The pole (vertical asymptote) moves from to .

4

Derivatives of Transforms

What if we multiply by instead of ?

Multiplying by in time corresponds to differentiating (and flipping sign) in s-domain.

5

Worked Examples

Example 1: Linearity

Find .

1. Separate Terms:

.

2. Use Table:

.

.

3. Combine:

.

Example 2: Translation

Find .

1. Identify Parts:

, shift is .

.

2. Apply Shift:

Replace every with .

.

.

Example 3: Derivative of Transform

Find .

1. Identify Formula:

.

2. Differentiate:

.

.

3. Combine signs:

.

6

Practice Quiz

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