42. Here is an interesting way to compute the Laplace trans- form of cos wt. (a) Using only Definition 1.1, show that L{sin t}(s) 1/(s² + 1). (b) Suppose that f (t) has Laplace transform F(s). Show that (;). L{f(at)}(s) = F - а a Use this property and the result found in part (a) to show that L{sin wt}(s) = s² + w² ° (c) If f (t) = sin wt, then f'(t) tion 2.1 to show that = w cos wt. Use Proposi- L{wcos wt}(s) = s2 + w² ' thus ensuring S L{cos wt}(s) : s2 + w² °

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Please focus on parts 42b and 42c. See pic 1 for the question and pic 2 for Proposition 2.1. Thank you.

42. Here is an interesting way to compute the Laplace trans-
form of cos wt.
(a) Using only Definition 1.1, show that L{sin t}(s)
1/(s² + 1).
(b) Suppose that f (t) has Laplace transform F(s). Show
that
LIf {at}{x) = =F (:)
1
L{f (at)}(s)
а
Use this property and the result found in part (a) to
show that
L{sin wt}(s) =
s2 + w² •
(c) If ƒ (t) = sin wt, then f'(t) = w cos wt. Use Proposi-
tion 2.1 to show that
= w coS wt. Use Proposi-
SW
L{wcos wt}(s) =
s² + w² '
thus ensuring
L{cos wt}(s)
||
s² + w?
Transcribed Image Text:42. Here is an interesting way to compute the Laplace trans- form of cos wt. (a) Using only Definition 1.1, show that L{sin t}(s) 1/(s² + 1). (b) Suppose that f (t) has Laplace transform F(s). Show that LIf {at}{x) = =F (:) 1 L{f (at)}(s) а Use this property and the result found in part (a) to show that L{sin wt}(s) = s2 + w² • (c) If ƒ (t) = sin wt, then f'(t) = w cos wt. Use Proposi- tion 2.1 to show that = w coS wt. Use Proposi- SW L{wcos wt}(s) = s² + w² ' thus ensuring L{cos wt}(s) || s² + w?
5.2 Basic Properties This section will discuss the most important properties of the Laplace transform.
of the Laplace We will state each property in a proposition.
Transform
The Laplace transform of derivatives
The most important property for our purposes is the relationship between the Laplace
transform and the derivative. As we will see, the next proposition is the key tool
when using the Laplace transform to solve differential equations.
PROPOSITION 2.1
Suppose y is a piecewise differentiable function of exponential order. Suppose also
that y' is of exponential order. Then for large values of s,
L(y')(s) = s L(y)(s) – y(0) = sY (s) – y(0),
(2.2)
where Y (s) is the Laplace transform of y.
Transcribed Image Text:5.2 Basic Properties This section will discuss the most important properties of the Laplace transform. of the Laplace We will state each property in a proposition. Transform The Laplace transform of derivatives The most important property for our purposes is the relationship between the Laplace transform and the derivative. As we will see, the next proposition is the key tool when using the Laplace transform to solve differential equations. PROPOSITION 2.1 Suppose y is a piecewise differentiable function of exponential order. Suppose also that y' is of exponential order. Then for large values of s, L(y')(s) = s L(y)(s) – y(0) = sY (s) – y(0), (2.2) where Y (s) is the Laplace transform of y.
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