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  • Perplex
    IB Math AAHL
    /
    Differential Equations
    /

    Solving Differential Equations

    Edit

    Exercises

    Key Skills

    Solving Differential Equations

    Solving Differential Equations

    An introduction to differential equations and how to solve them.

    Want a deeper conceptual understanding? Try our interactive lesson!

    Exercises

    No exercises available for this concept.

    Practice exam-style solving differential equations problems

    Key Skills

    Separable Variables
    AHL 5.18

    When you have a differential equation in the form

    ​
    dxdy​=f(x)g(y)🚫
    ​

    you can bring all the ​y​'s to one side and all the ​x​'s to the other:

    ​
    g(y)1​dy=f(x)dx🚫
    ​
    ​
    ∫g(y)1​dy=∫f(x)dx🚫
    ​


    Particular Solutions
    AHL 5.18

    The solutions to differential equations will usually contain a constant of integration ​+C. These are called general solutions.


    Often, we are given an initial condition, ie the value of ​y​ for a specific ​x, which we can use to solve for ​C. The result is the particular solution.

    Direct Integration
    AHL 5.18

    The easiest differential equations to solve are the ones in the form

    ​
    dxdy​=f(x)
    ​

    as we can simply integrate:

    ​
    y=∫f(x)dx🚫
    ​
    Integrating Factor
    AHL 5.18

    For a differential equation in the form

    ​
    dxdy​+P(x)y=Q(x)
    ​

    Multiply both sides by integrating factor (often called ​μ​):

    ​
    e∫P(x)dx📖
    ​

    and notice the product rule on the LHS.

    Homogeneous Equation
    AHL 5.18
    ​
    dxdy​=f(xy​)🚫
    ​


    Let ​y=vx, then ​v=xy​.


    Note: On IB exams you will be told to use the substitution ​y=vx.