Connected Rates of Change (Edexcel IAL Maths)

Spec point — 5.2

Connected rates of change

What are connected rates of change?

• In situations involving more than two variables you can use the chain rule to connect multiple rates of change into a single equation

• Equations involving derivatives (ie rates of changes) are known as differential equations

  • These can be solved using methods of integration (see Differential Equations )
  • However setting up the equation from the information given can involve the chain rule and connected rates of change

• Note from the examples above that you will often need to differentiate a formula to get one of the rates of change you need

Exam Hint

• These problems can involve a lot of letters – be sure to keep track of what they all refer to.
• Be especially sure that you are clear about which letters are variables and which are constants – these behave very differently when differentiation is involved!

Worked Example