How can I simplify these ODEs?

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In summary: Both of these forms can have derivatives (explicit form) or not (implicit form), and can be solved for (explicit form) or be given as a function (implicit form).
  • #1
gahara31
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Homework Statement


the first one
y'=[itex]\frac{y^{2}+xy^{2}}{x^{2}y-x^{2}}[/itex]

the second one
xyy'=[itex]\frac{x^{2}+1}{y+1}[/itex]

Homework Equations





The Attempt at a Solution


i separated x and y variable then integrate both of them

in the first one
∫[itex]\frac{y-1}{y^{2}}[/itex]dy=∫[itex]\frac{1+x}{x^{2}}[/itex]dx

ln|y|+[itex]\frac{1}{y}[/itex]+C=- [itex]\frac{1}{x}[/itex]+ln|x|+C

and the second one
∫y(y+1)dy = ∫[itex]\frac{x^{2}+1}{x}[/itex]dx

[itex]\frac{y^{3}}{3}[/itex]+[itex]\frac{y^{2}}{2}[/itex]+C=[itex]\frac{x^{2}}{2}[/itex]+ln|x|+C

but i can't change both of them into f(x) form or any simpler form
 
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  • #2
It is rare that you will find a differential equation with a solution that can be written as an explicit function. Implicit solutions, the equations relating x and y that you found, are usually accepted as finding a solution to a differential equation as well. As long as there are no derivatives in your final equation, and you specify the domain of the implicit function y that is defined by your equation, where it satisfies the original differential equation, you have found a solution.
Note, however, that you do not need two constants of integration: you may condense them into a single constant: C1 - C2 = C.
 
  • #3
slider142 said:
It is rare that you will find a differential equation with a solution that can be written as an explicit function. Implicit solutions, the equations relating x and y that you found, are usually accepted as finding a solution to a differential equation as well. As long as there are no derivatives in your final equation, and you specify the domain of the implicit function y that is defined by your equation, where it satisfies the original differential equation, you have found a solution.
Note, however, that you do not need two constants of integration: you may condense them into a single constant: C1 - C2 = C.

i see, i just don't really understand the difference between implicit and explicit form, so the thing i just solve is the implicit form.. thanks for answering
 
  • #4
The only thing to "understand" about "implicit" and "explicit" form is that the explicit form is always "y= some expression in x only" and the implicit form isn't!
 

FAQ: How can I simplify these ODEs?

Can you explain what an ODE is?

An ODE, or Ordinary Differential Equation, is a type of mathematical equation that relates a function and its derivatives. It is commonly used to model and solve problems in various fields, such as physics, engineering, and economics.

How do I know which method to use to solve an ODE?

The method used to solve an ODE depends on its type and complexity. Some common methods include separation of variables, integrating factors, and the method of undetermined coefficients. It is important to understand the characteristics of the ODE and choose the most appropriate method for the problem at hand.

Can you give an example of solving an ODE?

Sure, let's say we have the ODE dy/dx = x + 2. We can solve this using the method of separation of variables. First, we can rearrange the equation to get dy = (x + 2)dx. Then, we can integrate both sides to get y = (x^2/2) + 2x + C, where C is the constant of integration. This is the general solution to the ODE, and we can find the particular solution by substituting in any given initial conditions.

What are the applications of ODEs in real life?

ODEs have numerous applications in various fields. For example, they are used in physics to model the motion of objects under the influence of forces, in chemistry to describe chemical reactions, and in economics to model population growth and interest rates. They also have applications in engineering, biology, and other sciences.

Are there any software or tools that can help me solve ODEs?

Yes, there are many software and tools available that can help with solving ODEs. Some popular ones include MATLAB, Mathematica, and Maple. These programs have built-in functions and algorithms for solving ODEs, making the process easier and more efficient.

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