Quotient Rule (Cambridge O Level Additional Maths)

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Quotient Rule

What is the quotient rule?

  • The quotient rule is a formula that allows you to differentiate a quotient of two functions
    • i.e. one function divided by another
  • If bold italic y bold equals bold italic u over bold italic v where u and v are functions of x then the quotient rule is:
fraction numerator d y over denominator d x end fraction equals fraction numerator v fraction numerator d u over denominator d x end fraction minus u fraction numerator d v over denominator d x end fraction over denominator v squared end fraction

  • In function notation, if bold f bold left parenthesis bold italic x bold right parenthesis bold equals fraction numerator bold g bold left parenthesis bold italic x bold right parenthesis over denominator bold h bold left parenthesis bold italic x bold right parenthesis end fraction then the quotient rule can be written as:
begin mathsize 22px style straight f apostrophe left parenthesis x right parenthesis equals fraction numerator straight h left parenthesis x right parenthesis straight g apostrophe left parenthesis x right parenthesis minus straight g left parenthesis x right parenthesis straight h apostrophe left parenthesis x right parenthesis over denominator left parenthesis straight h left parenthesis x right parenthesis right parenthesis squared end fraction end style
  • As with the product rule, ‘dash notation’ may be used to make remembering it easier
y equals u over v
y apostrophe equals fraction numerator v u apostrophe minus u v apostrophe over denominator v squared end fraction
 
  • Final answers should match the notation used throughout the question

 

How do I know when to use the quotient rule?

  • The quotient rule is used when trying to differentiate a fraction where both the numerator and denominator are functions ofspace x
    • if the numerator is a constant, negative powers can be used
    • if the denominator is a constant, treat it as a factor of the expression\

 

How do I use the quotient rule?

  • Make it clear whatspace u comma space v comma space u apostrophe andspace v apostrophe are
    • arranging them in a square can help
      • opposite diagonals match up (like they do for product rule)
 STEP 1
 Identify the two functions,space u andspace v
 Differentiate bothspace u andspace v with respect tospace x to findspace u apostrophe andspace v apostrophe

 STEP 2
Obtain fraction numerator straight d y over denominator straight d x end fraction by applying the quotient rule formulaspace fraction numerator straight d y over denominator straight d x end fraction equals fraction numerator v fraction numerator straight d u over denominator straight d x end fraction minus u fraction numerator straight d v over denominator straight d x end fraction over denominator v squared end fraction
Be careful using the formula – because of the minus sign in the numerator, the order of the functions is important
Simplify the answer if straightforward or if the question requires a particular form


Quotient Rule Eg, AS & A Level Maths revision notes

 

Examiner Tip

  • The quotient rule formula is not on the list of formulas page – you have to memorise it
    • however if you do forget it in an exam, you could rewrite y equals u over v as y equals u cross times v to the power of negative 1 end exponent and then use the product rule
    • (the quotient rule is really doing exactly this)
  • Be careful using the formula – because of the minus sign in the numerator the order of the functions is important!

Worked example

Quotient Rule Example, AS & A Level Maths revision notes

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Amber

Author: Amber

Expertise: Maths

Amber gained a first class degree in Mathematics & Meteorology from the University of Reading before training to become a teacher. She is passionate about teaching, having spent 8 years teaching GCSE and A Level Mathematics both in the UK and internationally. Amber loves creating bright and informative resources to help students reach their potential.