Solving Exact Differential: x(dy/dx) = 2xe^x - y + 6x^2

In summary, the conversation is about a problem involving exact differentials. The problem is rearranged and partial derivatives are taken, but the result does not match the book's answer. The mistake is found to be a sign error in the rearranged equation.
  • #1
illidari
47
0

Homework Statement



x(dy/dx) = 2xe^x - y + 6x^2

Homework Equations





The Attempt at a Solution



I am trying to show this is an exact differential (book has an answer, it must be )

I rearranged the problem to be :

2xe^x - y + 6x^2 dx = x dy

Partial derivatives (using & for that symbol that represents partial)
&m/&y = -1
&m/&x = 1

-1 doesn't equal 1

Any idea where my mistake is?
 
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  • #2
illidari said:

Homework Statement



x(dy/dx) = 2xe^x - y + 6x^2

Homework Equations





The Attempt at a Solution



I am trying to show this is an exact differential (book has an answer, it must be )

I rearranged the problem to be :

2xe^x - y + 6x^2 dx = x dy

Partial derivatives (using & for that symbol that represents partial)
&m/&y = -1
&m/&x = 1

-1 doesn't equal 1

Any idea where my mistake is?
Write the equation as Mdx + Ndy = 0, and you'll see that this equation is exact, since My = Nx.
 
  • #3
*face palm*

Thank you lol :P

That would flip the sign of y and make it 1=1.
 

What is an exact differential equation?

An exact differential equation is a type of differential equation where the total differential of the equation can be expressed as the sum of two functions, one of which is the derivative of the other. In other words, the equation can be rewritten in the form of M(x,y)dx + N(x,y)dy = 0, where M and N are functions of x and y.

How do you solve an exact differential equation?

To solve an exact differential equation, you must first check if the equation is exact by verifying if the partial derivatives of M and N with respect to x and y are equal. If they are equal, you can then use the method of separation of variables to find a general solution. This involves rewriting the equation in the form of M(x,y)dx + N(x,y)dy = 0 and then integrating both sides with respect to x or y.

What is the specific solution to the equation x(dy/dx) = 2xe^x - y + 6x^2?

The specific solution to this exact differential equation is y = 6x^2 + Cx + 2e^x, where C is a constant. This can be found by using the method of separation of variables and integrating both sides with respect to x.

What is the significance of solving exact differential equations?

Solving exact differential equations is important in various fields of science and engineering, as it allows us to model and understand the behavior of complex systems. It is particularly useful in physics, chemistry, and economics, among other disciplines, where many natural processes can be described by differential equations.

Can exact differential equations have multiple solutions?

Yes, exact differential equations can have multiple solutions. This is because when solving the equation, we usually have to integrate both sides, and the integration constant can take on different values, resulting in different solutions. In some cases, there may also be a family of solutions that can be expressed in terms of arbitrary functions.

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