What are the steps to solve an exact differential equation once you've confirmed it's exact?
Conditions
- The differential equation has been verified as exact.
Reasoning, step by step
- Integrate with respect to x, adding an arbitrary function of y, .
- Integrate with respect to y, adding an arbitrary function of x, .
- Compare the two expressions for to determine the unknown functions and .
- Combine the unique terms from both integrations to form the final potential function.
- Set the potential function equal to a constant C to get the implicit solution.
Example
For the equation (-3x^2 - y), integrating M gives -x^3 - xy + and integrating N gives - xy + . Combining these yields the solution -x^ - xy = C.
Common misconceptions
- Forgetting to include the arbitrary functions of integration.
- Double-counting terms that appear in both integrations.
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Related questions
The final implicit solution for the example equation (-3x^2 - y) is -x^ - xy = C.
Conditions: The equation is exact.; The terms are combined correctly without double-counting.
The term -xy appears in both the integration of M with respect to x and the integration of N with respect to y. When combining the results to form the potential function, shared terms should only be included once to avoid double-counting.
Conditions: The term -xy is present in both antiderivatives.
When integrating a multivariable function with respect to one variable, the other variables are treated as constants. Therefore, the 'constant' of integration can be any function that depends only on the other variables, which in this case is y.
Conditions: The integration is with respect to x.; The function M depends on both x and y.
The presenter leaves the answer in implicit form because the equation contains multiple powers and products of y, making it cumbersome to solve explicitly for y.
Conditions: The solution contains multiple y terms.; An explicit solution for y is not attempted.
To check if a differential equation is exact, you must verify that the partial derivative of the coefficient of dx with respect to y is equal to the partial derivative of the coefficient of dy with respect to x. If these mixed partial derivatives are equal, the equation is exact.
Conditions: The equation must be in the form .; M and N must have continuous first-order partial derivatives.
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