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Perplex
Perplex
Dashboard
Topics
Exponents & LogarithmsApproximations & ErrorSequences & SeriesCounting & BinomialsProof and ReasoningComplex NumbersAlgebra Skills
Cartesian plane & linesQuadraticsFunction TheoryTransformations & asymptotesPolynomials
2D & 3D GeometryTrig equations & identitiesVectors
ProbabilityDescriptive StatisticsBivariate StatisticsDistributions & Random Variables
DifferentiationIntegrationDifferential EquationsMaclaurin
Review VideosFormula BookletMy Progress
BlogLanding Page
Sign UpLogin
Perplex
IB Math AAHL
/
Differential Equations
/
Skills
Edit

Skill Checklist

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

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

IB Math AAHL
/
Differential Equations
/
Skills
Edit

Skill Checklist

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

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

Skill Checklist

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

7 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
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🚫
​
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
​

And then integrate:

​
∫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.

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​​ and ​dxdy​=v+x⋅dxdv​.


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

Euler's Method

2 skills
The Idea Behind Euler's Method
AHL 5.18

When we have a differential equation of the form ​dxdy​=f(x,y), Euler's Method enables us to estimate the value of ​y​ for a specific ​x​ by starting with a known point and taking small steps towards the ​x​-value we are interested in.


It works like this:

  1. Start at the known point.

  2. Find the slope at the current point.

  3. Take a horizontal step of size ​h​

  4. Take a vertical step of size ​h​ times the slope found in 2.

  5. Repeat 2-5 until the desired ​x​-value is reached.

This is useful because in the physical world, we often know the state in which a system starts, and we have equations that model how the system will change.


It is very common for these physical models not to have exact solutions, so we need to use numerical methods, of which Euler's Method is one example.

Performing Euler's Method
AHL 5.18

Euler's Method is a technique for approximating numerical solutions to differential equations by taking small steps in the ​x​ and ​y​ directions in accordance with the differential equation.


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​)📖​

Skill Checklist

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

7 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
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🚫
​
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
​

And then integrate:

​
∫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.

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​​ and ​dxdy​=v+x⋅dxdv​.


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

Euler's Method

2 skills
The Idea Behind Euler's Method
AHL 5.18

When we have a differential equation of the form ​dxdy​=f(x,y), Euler's Method enables us to estimate the value of ​y​ for a specific ​x​ by starting with a known point and taking small steps towards the ​x​-value we are interested in.


It works like this:

  1. Start at the known point.

  2. Find the slope at the current point.

  3. Take a horizontal step of size ​h​

  4. Take a vertical step of size ​h​ times the slope found in 2.

  5. Repeat 2-5 until the desired ​x​-value is reached.

This is useful because in the physical world, we often know the state in which a system starts, and we have equations that model how the system will change.


It is very common for these physical models not to have exact solutions, so we need to use numerical methods, of which Euler's Method is one example.

Performing Euler's Method
AHL 5.18

Euler's Method is a technique for approximating numerical solutions to differential equations by taking small steps in the ​x​ and ​y​ directions in accordance with the differential equation.


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​)📖​