Solving ln x for x: ce^{-0.03t}

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SUMMARY

The discussion focuses on the mathematical derivation of the equation x = ce^{-0.03t} from ln x = -0.03t + c'. The transformation involves recognizing that e^{c'} is a constant, denoted as c, which can be determined using initial conditions. The incorrect assumption that x could be expressed as e^{-0.03t} + c is clarified, emphasizing the need for multiplication rather than addition in the exponential form. The derivation is crucial for solving differential equations involving exponential decay.

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How does one get from [itex]ln x = -0.03t + c'[/itex] to [itex]x = ce^{-0.03t}[/itex]

Why isn't it [itex]x = e^{-0.03t} + c[/tex]? where [itex]c = e^{c'}[/itex][/itex]
 
Last edited:
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cscott said:
How does one get from [itex]ln x = -0.03t + c'[/itex] to [itex]x = ce^{-0.03t}[/itex]

Why isn't it [itex]x = e^{-0.03t} + c[/tex]? where [itex]c = e^{c'}[/itex][/itex]
[itex] <br /> Well, it cannot be your equation for x, the + should be *<br /> <br /> Look at this derivation :<br /> <br /> [tex]ln x = -0.03t + c'[/tex]<br /> <br /> [tex]x = e^{-0.03t + c'}[/tex]<br /> <br /> [tex]x = e^{-0.03t} * e^{c'}[/tex]<br /> <br /> They called the [tex]e^{c'}[/tex] the constant c.<br /> <br /> This can be done since you this constant must be determined using some given initial conditions like at t = 0, x must be 5 or so...<br /> <br /> marlon<br /> <br /> EDIT : if you want you can just use [tex]e^{c'}[/tex] as well, it does not really matter because of the way the constant must be calculated. The result will be the same.[/itex]
 
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Thanks marlon. :)
 

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