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  • Perplex
    IB Math AAHL
    /
    Differential Equations
    /

    Skills

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    Skill Checklist

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    Skill Checklist

    Track your progress across all skills in your objective. Mark your confidence level and identify areas to focus on.

    6 Skills Available

    Track your progress:

    Don't know

    Working on it

    Confident

    📖 = included in formula booklet • 🚫 = not in formula booklet

    Track your progress:

    Don't know

    Working on it

    Confident

    📖 = included in formula booklet • 🚫 = not in formula booklet

    Solving Differential Equations

    5 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.

    Euler's Method

    1 skill
    Performing Euler's Method
    AHL 5.18

    Mathematically Euler's Method works as follows:

    1. Start at a known point ​(x0​,y0​)​

    2. Pick a step size ​h​ such that ​x0​+nh=xfinal​​ for some integer ​n.

    Repeat the following steps for each ​n​ until the desired ​x​-value is reached:

    1. Find the slope ​dxdy​=f(xn​,yn​)​

    2. Find the next ​x​ value ​xn+1​=xn​+h📖.

    3. Find the next ​y​-value ​yn+1​=yn​+h×f(xn​,yn​)📖​