Solving Separable DE with Initial Value: Techniques and Examples

  • Thread starter Jeann25
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In summary, the conversation discusses a problem with dividing by y in the equation y'=xy/(1+x²). The correct solution involves using logarithms and simplifying the expression to get the answer of c*sqrt(1+x²).
  • #1
Jeann25
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How would I start this one? I tried dividing by y, but that does not work

y'=xy/(1+x²)
 
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  • #2
Why doesn't that work?
 
  • #3
Jeann25 said:
How would I start this one? I tried dividing by y, but that does not work

y'=xy/(1+x²)

Yeah why does dividing by y not work?
 
  • #4
Here's what I did:

1/y y' = x/(1+x²)
ln y = 1/2 ln (1+x²)+c
y = ce^(1/2 ln(1+x²))

Answer's supposed to be: c*sqrt(1+x²)
 
  • #5
Jeann25 said:
Here's what I did:

1/y y' = x/(1+x²)
ln y = 1/2 ln (1+x²)+c
y = ce^(1/2 ln(1+x²))

Answer's supposed to be: c*sqrt(1+x²)

Yeah, ok and how is that different from what you had? Just simplify your expression with the properties of logs.
 
  • #6
Nevermind. I get it now. Thank you :)
 

1. What is a separable differential equation?

A separable differential equation is a type of ordinary differential equation (ODE) in which the dependent variable and independent variable can be separated into two separate functions. This allows for the equation to be solved by integrating both sides separately.

2. What techniques are used to solve separable differential equations?

The main technique used to solve separable differential equations is separation of variables. This involves isolating the dependent and independent variables on opposite sides of the equation, and then integrating both sides. Other techniques such as substitution and partial fractions may also be used in some cases.

3. What is the initial value in a separable differential equation?

The initial value in a separable differential equation is a specific set of conditions given at the starting point of the problem. This includes the initial value of the dependent variable and the value of the independent variable at the starting point. These values are used to find the particular solution to the equation.

4. Can you provide an example of solving a separable differential equation with initial value?

Sure! For example, let's say we have the separable differential equation dy/dx = x/y with the initial condition y(1) = 2. First, we can rewrite the equation as ydy = xdx. Then, we can integrate both sides to get (y^2)/2 = (x^2)/2 + C. Plugging in the initial value, we get (2^2)/2 = (1^2)/2 + C, which simplifies to C = 1. Therefore, the particular solution to the equation is (y^2)/2 = (x^2)/2 + 1.

5. What are some real-world applications of separable differential equations?

Separable differential equations are used to model a variety of natural phenomena in fields such as physics, chemistry, biology, and economics. For example, they can be used to describe the rate of growth of a population, the spread of an infectious disease, or the cooling of a hot object. They are also commonly used in engineering applications to predict the behavior of systems and optimize designs.

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