Solve the separable differential equation

In summary, the conversation discusses the solution to the equation dx/dy=-0.6y with initial condition y(0)=5. The attempt at solving the problem involves taking the integral of both sides and using initial conditions to find the constant of integration. However, the mistake is made in substituting the initial condition before solving for the function, resulting in an incorrect solution. The correct solution is y=5e^{-0.6x}.
  • #1
hardatwork
9
0

Homework Statement



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

Homework Equations





The Attempt at a Solution


I tried solving it by
[tex]\int[/tex]dy/y=[tex]\int[/tex]-0.6dx
ln(y)=-0.6x+c
ln(y(0))=-0.6(0)+c
ln(5)=c
ln(y)=-0.6x+ln(5)
y=[tex]e^{-0.6x}[/tex]+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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  • #2
You should solve for your function before substituting initial conditions. Remember that [tex]e^{ln|y|}=y[/tex]
 
  • #3
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?

[tex]\int[/tex]dy/y=[tex]\int[/tex]-0.6dx
ln(y)=-0.6x+c
ln(y(0))=-0.6(0)+c
ln(5)=c
ln(y)=-0.6x+ln(5)
y=[tex]e^{-0.6x}[/tex]+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 [itex]\ln y=-0.6x+\ln 5[/itex], then

[tex]y=e^{-0.6x+\ln 5}=e^{\ln 5}e^{-0.6x}=5e^{-0.6x}\neq e^{-0.6x}+5[/tex]
 
  • #4
Okay. That makes so much sense. Thank You so much
 

1. What is a separable differential equation?

A separable differential equation is a type of differential equation that can be expressed in the form of two separate functions multiplied together, where one function contains only the dependent variable and the other contains only the independent variable. This allows for the equation to be separated and solved more easily.

2. How do I know if an equation is separable?

An equation is separable if it can be written in the form of dy/dx = g(x)f(y), where g(x) and f(y) are functions of x and y, respectively. In other words, if the dependent and independent variables can be separated on opposite sides of the equation, then it is separable.

3. What is the general method for solving a separable differential equation?

The general method for solving a separable differential equation is to separate the variables, integrate both sides, and then solve for the dependent variable. This usually involves using the chain rule to integrate the left side of the equation and applying the fundamental theorem of calculus to integrate the right side.

4. Can all differential equations be solved using separation of variables?

No, not all differential equations can be solved using separation of variables. This method only works for equations that are separable, so it cannot be used for equations that do not have this form. Additionally, some separable equations may require more advanced techniques to solve.

5. Are there any tips for solving separable differential equations?

Yes, there are a few tips that can help make solving separable differential equations easier. First, always check if the equation is separable before attempting to solve it. Second, it can be helpful to rewrite the equation in a more simplified form before separating the variables. And finally, be sure to check your solution by plugging it back into the original equation to ensure it satisfies the equation.

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