Solve the separable differential equation

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SUMMARY

The separable differential equation dx/dy = -0.6y with the initial condition y(0) = 5 was incorrectly solved by the user. The correct approach involves recognizing that the solution should be y = 5e^{-0.6x}, not y = e^{-0.6x} + 5. The user initially misapplied the properties of logarithms and exponentials, leading to an incorrect final expression. Clarification on the correct manipulation of the equation was provided by other forum members.

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hardatwork
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Homework Statement



dx/dy=-0.6y
y(0)=5

Homework Equations





The Attempt at a Solution


I tried solving it by
\intdy/y=\int-0.6dx
ln(y)=-0.6x+c
ln(y(0))=-0.6(0)+c
ln(5)=c
ln(y)=-0.6x+ln(5)
y=e^{-0.6x}+5
But its incorrect. I don't know what I am doing wrong. Can someone helping see what I am doing wrong? Thank You so much!
 
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You should solve for your function before substituting initial conditions. Remember that e^{ln|y|}=y
 
hardatwork said:

Homework Statement



dx/dy=-0.6y

Is this a typo? Do really mean dx/dy=-0.6y, or do you mean dy/dx=-0.6y?

\intdy/y=\int-0.6dx
ln(y)=-0.6x+c
ln(y(0))=-0.6(0)+c
ln(5)=c
ln(y)=-0.6x+ln(5)
y=e^{-0.6x}+5
But its incorrect. I don't know what I am doing wrong. Can someone helping see what I am doing wrong? Thank You so much!

If \ln y=-0.6x+\ln 5, then

y=e^{-0.6x+\ln 5}=e^{\ln 5}e^{-0.6x}=5e^{-0.6x}\neq e^{-0.6x}+5
 
Okay. That makes so much sense. Thank You so much
 

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