Bernoulli Differential Equation

Then du= -3y^2 dyso\frac{y^2 dy}{1- y^3}= \frac{-du}{3}and \frac{dx}{x}= \int \frac{-du}{3}= -\frac{1}{3}u+ C= -\frac{1}{3}(1- y^3)+ C= \frac{y^3- 1}{3}+ C So\frac{y^2}{3}+ C= \frac{y^3- 1}{3}y^3- y^2- 3+ C= 0y^2(y- 1)= 3- C
  • #1
bdh2991
103
0

Homework Statement



solve the given differential equation: xdy/dx + y = y^-2

Homework Equations


The Attempt at a Solution



I don't understand how to do these substitutions...i got n=-2 then u=y^3, du/dx=3y^2

from there i don't know where to place them
 
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  • #2
It probably doesn't make sense partially because you didn't calculate du/dx correctly. You're differentiating with respect to x, not y, so you need to use the chain rule:
$$\frac{du}{dx} = 3y^2\frac{dy}{dx}$$

Now, first, divide the differential equation by x so that the coefficient of y' is 1. Then get rid of the y's from the righthand side by multiplying by y2. You end up with
$$y^2\frac{dy}{dx} + \frac{1}{x} y^3 = \frac{1}{x} $$ Now write that in terms of u=y3 and u'.
 
  • #3
You can also note that this is a separable equation:
[tex]x\frac{dy}{dx}+ y= y^{-2}[/tex]
[tex]x\frac{dy}{dx}= -y+ y^{-2}[/tex]
[tex]\frac{dy}{-y+ y^{-2}}= \frac{dx}{x}[/tex]
[tex]\frac{y^2 dy}{1- y^3}= \frac{dx}{x}[/tex]

To integrate on the left, let [itex]u= 1- y^3[/itex].
 

Related to Bernoulli Differential Equation

1. What is a Bernoulli Differential Equation?

A Bernoulli Differential Equation is a type of differential equation that can be written in the form dy/dx + P(x)y = Q(x)y^n, where y is the dependent variable, x is the independent variable, P(x) and Q(x) are functions of x, and n is any real number except 0 and 1.

2. What is the significance of Bernoulli Differential Equations in science?

Bernoulli Differential Equations are important in science because they can be used to model a wide range of physical phenomena, such as population growth, chemical reactions, and fluid dynamics. They also have applications in engineering, economics, and other fields.

3. How do you solve a Bernoulli Differential Equation?

To solve a Bernoulli Differential Equation, you can use a substitution method to transform the equation into a linear differential equation, which can then be solved using standard techniques such as separation of variables or integrating factors. Alternatively, you can use the Bernoulli equation method, which involves dividing both sides of the equation by y^n and then making a substitution.

4. Can Bernoulli Differential Equations have multiple solutions?

Yes, Bernoulli Differential Equations can have multiple solutions. This is because the equation contains a power of y, and different values of n can result in different solutions. In some cases, there may also be multiple solutions for a given value of n.

5. How are Bernoulli Differential Equations related to other types of differential equations?

Bernoulli Differential Equations are a special case of nonlinear differential equations, as they involve a nonlinear term (y^n). They are also closely related to linear differential equations, as they can be transformed into linear equations using appropriate substitutions. Additionally, Bernoulli Differential Equations are a type of first-order differential equation, which means they involve only the first derivative of the dependent variable.

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