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What are the steps to solve an exact differential equation once you've confirmed it's exact?

The steps involve finding the potential function F(x,y)F(x,y) by integrating M with respect to x and N with respect to y, then combining the results to form the implicit solution F(x,y)=CF(x,y) = C.

Conditions

  • The differential equation has been verified as exact.

Reasoning, step by step

  1. Integrate M(x,y)M(x,y) with respect to x, adding an arbitrary function of y, c1(y)c_1(y).
  2. Integrate N(x,y)N(x,y) with respect to y, adding an arbitrary function of x, c2(x)c_2(x).
  3. Compare the two expressions for F(x,y)F(x,y) to determine the unknown functions c1(y)c_1(y) and c2(x)c_2(x).
  4. Combine the unique terms from both integrations to form the final potential function.
  5. Set the potential function equal to a constant C to get the implicit solution.

Example

For the equation (-3x^2 - y)dx+(3y2−x)dy=0dx + (3y^2 - x)dy = 0, integrating M gives -x^3 - xy + c1(y)c_1(y) and integrating N gives y3y^3 - xy + c2(x)c_2(x). Combining these yields the solution -x^3+y33 + y^3 - xy = C.

Common misconceptions

  • Forgetting to include the arbitrary functions of integration.
  • Double-counting terms that appear in both integrations.

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