Laplace Transform for Functions: 5cos(7t+π/4) and e^(3t)sintcost

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SUMMARY

The discussion focuses on finding the Laplace transforms for the functions 5cos(7t + π/4) and e^(3t)sin(t)cos(t). For the first function, the Laplace transform can be computed using the cosine addition formula, which simplifies the expression before applying the standard Laplace transform formula. The second function requires the application of the Laplace transform properties for products of functions. The identity f(t)' = sF(s) + f(0) is referenced but not fully utilized in the solutions provided.

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  • Understanding of Laplace transforms and their properties
  • Familiarity with trigonometric identities, specifically the cosine addition formula
  • Knowledge of exponential functions and their transformations
  • Basic calculus concepts, including derivatives and initial conditions
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  • Study the application of the cosine addition formula in Laplace transforms
  • Learn about the Laplace transform of products of functions, particularly e^(at)sin(bt)
  • Explore the use of initial conditions in solving differential equations using Laplace transforms
  • Review the properties of Laplace transforms, including linearity and shifting theorems
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Students studying differential equations, mathematicians, and engineers looking to understand Laplace transforms for complex functions.

skrat
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Homework Statement


Find Laplace transformation for functions ##f(t)##:
a) ##5cos(7t+\pi /4)##
b) ##e^{3t}sintcost##

Homework Equations


The Attempt at a Solution



a) I know that for ##cos(\omega t)## the laplace is ##\frac{s}{s^2+\omega ^2}## but what can I do with that ##\pi /4## ?

I believe I would have to use this identity ##f(t)^{'}=sF(s)+f(0)## but I don't know how o use it...

Could somebody please show me that?
 
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skrat said:

Homework Statement


Find Laplace transformation for functions ##f(t)##:
a) ##5cos(7t+\pi /4)##
b) ##e^{3t}sintcost##


Homework Equations





The Attempt at a Solution



a) I know that for ##cos(\omega t)## the laplace is ##\frac{s}{s^2+\omega ^2}## but what can I do with that ##\pi /4## ?

I believe I would have to use this identity ##f(t)^{'}=sF(s)+f(0)## but I don't know how o use it...

Could somebody please show me that?

Use the addition formula for ##\cos(a+b)## before taking the transform.
 
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OMG, How can I be so stupid! -.-

Thanks LCKurtz!
 

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