Finding Areas Between Lines & Curves (Cambridge O Level Additional Maths)

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Area Between a Curve & a Line

How do I find the area between a curve and a line?

  • The area enclosed will be the difference between …
    • the area under the line and
    • the area under the curve

Area between a curve and a line

  • These can be found separately

Splitting an area up

  • STEP 1
    •  Find the intersections of the line and the curve (if not given)
  • STEP 2
    • Find the area under a curve, RC, using definite integration
  • STEP 3 
    • Find the area under a line, RL, either using definite integration or the area formulae for basic shapes
  • STEP 4 
    • To find the area, R, between the curve and the line subtract the smaller area from the larger area
    • If curve on top this will be RC – RL
    • If line on top this will be RL - RC
  • There may be easier ways to find the area under a line

 Shortcuts for finding areas under a line using rectangles, triangles and trapeziums

Can I subtract before integrating?

  • Yes - see the next note on "Area between two curves"
  • Essentially you treat the line as a second curve 
    • It can be easier to make mistakes using this method

Examiner Tip

  • Add information to any diagram provided
    • Add axes intercepts, as well as intercepts between lines and curves
  • Mark and shade the area you’re trying to find
  • If no diagram is provided, sketch one!

Worked example

Example Question fig1, A Level & AS Level Pure Maths Revision NotesExample fig2, A Level & AS Level Pure Maths Revision NotesExample fig3, AS & A Level Maths revision notesExample fig4, AS & A Level Maths revision notes

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Area Between Two Curves

What is the area between two curves?

  • In general find the definite integral of “upper curve” – “lower curve”
  • However this does depend on …
    • … the area being found
    • … if the curves intersect (and cross over)

Area between two curves

  • The area may have to be split into separate integrals

 Area between two intersecting curves 

  • The points at which curves intersect may need to be calculated

How do I find the area between two curves?

  • STEP 1
    • Find the intersections of the curves if needed
  • STEP 2
    •  Form the integral …
      • … using the intersections as limits
      • … “upper curve” – “lower curve” …
      • … and find the value of the integral
  • STEP 3
    • Repeat STEP 2 if more than one area needed
  • STEP 4
    • Add areas together

Example of area between two curvesUsing integration to find the area between two curves

Examiner Tip

  • If no diagram is provided sketch one, even if the curves are not accurate
  • Add information to any given diagram as you work through a question

Worked example

Example quest, AS & A Level Maths revision notesExample soltn, A Level & AS Level Pure Maths Revision Notes

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Paul

Author: Paul

Expertise: Maths

Paul has taught mathematics for 20 years and has been an examiner for Edexcel for over a decade. GCSE, A level, pure, mechanics, statistics, discrete – if it’s in a Maths exam, Paul will know about it. Paul is a passionate fan of clear and colourful notes with fascinating diagrams – one of the many reasons he is excited to be a member of the SME team.