DE Exactness: (2x+y)dx-(x+6y)dy=0?

  • Thread starter Eastonc2
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In summary, the conversation discusses determining whether a given differential equation is exact or not. There is confusion about the definition of an exact DE and how to determine if it matches the given equation. The participants suggest finding a function that matches the partial derivatives of M(x,y) and N(x,y) to clarify the situation.
  • #1
Eastonc2
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Homework Statement


determine whether the DE, (2x+y)dx-(x+6y)dy=0, is exact

Homework Equations


i understand how to determine if they are exact, I just don't understand this specific instance. for my case, M(x,y)=2x+y, but would N(x,y)=(x+6y), or (-x-6y)?

The Attempt at a Solution


using my first N(x,y), the equation is exact, however, using the second, they are not exact.

Just need clarification at this point
 
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  • #2
Hi Eastonc2! :smile:

Your N(x,y)=(-x-6y).
That is how it matches the definition of an exact DE.

But how did you determine that it was exact with the first N(x,y)?
Because I don't think it is.
 
  • #3
ah, my fault, M(x,y)=2x+y

i was looking at the equation above it for that first part. the second part is correct though.
 
  • #4
Ah, now I see your dilemma.

To make sure, perhaps you should try to find a function of which the partial derivatives match with M(x,y) and N(x,y).
Can you find such a function?
 
  • #5
Have you studied the case where M and N are homogeneous of the same degree, as these are?
 

What is the definition of "exactness" in terms of differential equations?

Exactness in differential equations refers to a specific property where the total differential of a function can be expressed as the sum of its partial derivatives. In other words, the differential equation is considered exact if it satisfies the condition of being closed.

How can you determine if a given differential equation is exact?

To determine if a differential equation is exact, you can use the method of checking for exactness, which involves checking if the partial derivatives of the given equation are equal. If they are equal, then the equation is exact. Another method is to use the integrating factor, which is a function that can be multiplied to the given equation to make it exact.

What is the importance of exactness in solving differential equations?

Exactness is important in solving differential equations because it allows us to find the general solution to the equation. It also helps in simplifying the process of solving the equation by using the integrating factor method. Additionally, exactness is a necessary condition for a differential equation to have a solution.

Can a non-exact differential equation be made exact?

Yes, a non-exact differential equation can be made exact by using the integrating factor method. This method involves finding a function that can be multiplied to the given equation to make it exact. The integrating factor can be determined by solving a first-order linear differential equation.

How is exactness related to the concept of "closed" in multivariable calculus?

Exactness in differential equations is closely related to the concept of "closed" in multivariable calculus. In both cases, the term "closed" refers to the property of a function or equation where the total change in a given quantity is equal to the sum of its partial changes. In multivariable calculus, this is referred to as a closed path integral, while in differential equations, it is called an exact differential.

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