Change of Sign Method (Edexcel A Level Maths): Revision Note

Change of Sign

What does a change of sign mean?

• A sign change between f(a) to f(b) means there must be a root between a and b

• When an equation cannot be solved using the usual analytical methods, we can use change of sign to find approximate solutions

• We can say a root lies within a particular interval or is correct to a given accuracy

• Bounds can be used to show a root is correct

• Using sign change to find a root is only appropriate for continuous functions in a small interval