Laplace Transform of Cosine and Hyperbolic Cosine

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SUMMARY

The Laplace Transform of the product of cosine and hyperbolic cosine, L[cos(at)cosh(at)], is established as (s^3)/(s^4 + 4a^4). The discussion emphasizes the use of the first shift property and clarifies that Euler's formula for cosine does not equate cos(at) with cosh(at). Instead, the correct representation involves complex exponentials, specifically cos(at) = (e^(iat) + e^(-iat))/2. This distinction is crucial for obtaining the correct Laplace Transform.

PREREQUISITES
  • Understanding of Laplace Transforms, specifically L[cos(at)] = s/(s^2 + w^2)
  • Familiarity with hyperbolic functions, particularly cosh(at)
  • Knowledge of Euler's formula for complex exponentials
  • Experience with the first shift property in Laplace Transforms
NEXT STEPS
  • Study the first shift property in Laplace Transforms for various functions
  • Learn about the application of Euler's formula in transforming trigonometric functions
  • Explore the derivation of Laplace Transforms for products of functions
  • Investigate the implications of complex numbers in Laplace Transform calculations
USEFUL FOR

Students studying differential equations, engineers applying Laplace Transforms in control systems, and mathematicians exploring the properties of transforms involving trigonometric and hyperbolic functions.

chickens
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Homework Statement



L[cos(at)cosh(at)] = ?


Homework Equations



L[cos(at)] = s/(s^2 + w^2)



The Attempt at a Solution



I'm able to get the solution given that is (s^3)/(s^4 + 4a^4)

The question requested to use first shift property. So I used cosh(at) = 1/2[e^at + e^(-at)]

but now I'm trying to use another method.

if you use euler's rule, you can also get cos(at) = cosh(at) = 1/2[e^at + e^(-at)]

then simply multiply them and get L[e^2at + 2 + e^(-2at)] but I don't seem to get the same solution as above, any ideas? :frown:
 
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chickens said:

Homework Statement



L[cos(at)cosh(at)] = ?


Homework Equations



L[cos(at)] = s/(s^2 + w^2)



The Attempt at a Solution



I'm able to get the solution given that is (s^3)/(s^4 + 4a^4)

The question requested to use first shift property. So I used cosh(at) = 1/2[e^at + e^(-at)]

but now I'm trying to use another method.

if you use euler's rule, you can also get cos(at) = cosh(at) = 1/2[e^at + e^(-at)]
No, Euler's rule does NOT say cos(at)= cosh(at)!
You may be thinking of
cos(at)= \frac{e^{iat}+ e^{-iat}}{2}
Note the "i" s in that!

then simply multiply them and get L[e^2at + 2 + e^(-2at)] but I don't seem to get the same solution as above, any ideas? :frown:
 

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