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  • Perplex
    IB Math AAHL
    /
    Differential Equations
    /

    Skills

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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:

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    Working on it

    Confident

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

    Track your progress:

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    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​)📖