Dy/dx +( y/x ) = x(y^3)

  • Thread starter hotjohn
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In summary, the conversation discusses a differential equation with a wrong answer and the asker is seeking help in identifying which part of their working is incorrect. The responder also provides an alternative method for solving the differential equation.
  • #1
hotjohn
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1

Homework Statement


i am given dy/dx +( y/x ) = x(y^3) , using transformation of function = y=v/x , but my ans is wrong , which part of my working is wrong ?

Homework Equations

The Attempt at a Solution

 

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  • #2
hotjohn said:

Homework Statement


i am given dy/dx +( y/x ) = x(y^3) , using transformation of function = y=v/x , but my ans is wrong , which part of my working is wrong ?

Homework Equations

The Attempt at a Solution

It's very difficult to read your images.

Can you type them out?
 
  • #3
SammyS said:
It's very difficult to read your images.

Can you type them out?
Which part of the working that you can't read?
 
  • #4
hotjohn said:
Which part of the working that you can't read?
None of it is easy to read.

I did zoom in & struggled through.

When you substitute back in for v (to eliminate v) what did you plug in ?From now on, please try to follow the forum rules more closely.
 
  • #5
SammyS said:
None of it is easy to read.

I did zoom in & struggled through.

When you substitute back in for v (to eliminate v) what did you plug in ?From now on, please try to follow the forum rules more closely.

ok , thanks for pointing out my mistake
 
  • #6
This is actually a really cool problem, it's a "Reverse" homogeneous equation.
 
  • #7
There is another method to solve this Differential equation is by converting it to exact form

multiply the whole equation by xdx

=> ## xdy + ydx = x^2y^3dx ##
now multiply and divide by x on RHS

## xdy + ydx = (xy)^3(dx/x) ##

now using xdy + ydx = d(xy)

## \frac {d(xy)} {(xy)^3} = \frac {dx} {x} ##

## \int \frac {d(xy)} {(xy)^3} = \int \frac {dx} {x} ##

now it is easily integrable
 
Last edited:

1. What is the equation "Dy/dx + (y/x) = x(y^3)" called?

The equation "Dy/dx + (y/x) = x(y^3)" is a first-order linear differential equation.

2. How do you solve the equation "Dy/dx + (y/x) = x(y^3)"?

To solve the equation "Dy/dx + (y/x) = x(y^3)", you can use the method of integrating factors. First, rearrange the equation to the form dy/dx + P(x)y = Q(x), where P(x) = 1/x and Q(x) = x(y^3). Then, multiply both sides by the integrating factor μ(x) = e^(∫P(x)dx), which in this case is μ(x) = e^(∫1/x dx) = e^lnx = x. This gives the equation x(dy/dx) + (xy/x) = x^2(y^3). The left side can now be simplified to d(xy)/dx, and the right side can be integrated with respect to x. Finally, solve for y to get the general solution.

3. Can the equation "Dy/dx + (y/x) = x(y^3)" be solved with separation of variables?

No, the equation "Dy/dx + (y/x) = x(y^3)" cannot be solved with separation of variables because it is not in the form dy/dx = f(x)g(y). Instead, it is a first-order linear differential equation, which requires the method of integrating factors to solve.

4. What is the solution to the equation "Dy/dx + (y/x) = x(y^3)"?

The solution to the equation "Dy/dx + (y/x) = x(y^3)" is y = (c + 1/x^2)^(1/3), where c is a constant. This is the general solution obtained through the method of integrating factors.

5. What is the significance of the equation "Dy/dx + (y/x) = x(y^3)" in mathematics?

The equation "Dy/dx + (y/x) = x(y^3)" is a first-order linear differential equation, which is a fundamental concept in differential equations and is used to model many real-world phenomena in various fields of science and engineering. Solving this equation allows us to understand and predict how certain variables change over time, which is crucial in making important decisions and advancements in our understanding of the world.

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