Modelling with Differential Equations (OCR A Level Maths A) : Revision Note
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Modelling with Differential Equations
What can be modelled with differential equations?
Derivative terms like
are “rates of change”
There are many situations that involve “change”
Temperature
Radioactivity
Medication
Sales

How do I set up a model with differential equations?
The first task is to set up a differential equation from a description in words:

Important phrases here are …
… “rate of change” ... reference to a derivative term like
… directly/inversely proportional to ...
,
… formulate ... means to write as an equation
you may need to choose and define letters for variables
V for volume, h for height (of a cylinder, say)
Some differential equations may involve Connected Rates of Change

Examiner Tips and Tricks
Use a highlighter (or underline) to pick out important words/phrases
Read and re-read the question several times
Jot down bits and pieces as you go; do not expect to go straight from reading to writing down a differential equation.
Worked Example

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