Hyperbolic Functions & Graphs (Edexcel A Level Further Maths: Core Pure)

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Hyperbolic Functions & Graphs

What are the definitions of the hyperbolic functions?

  • Hyperbolic sine 

sin text h end text x equals 1 half open parentheses straight e to the power of x minus straight e to the power of negative x end exponent close parentheses

    • This can be pronounced "shine" or "sinch"
  • Hyperbolic cosine 

cosh x equals 1 half open parentheses straight e to the power of x plus straight e to the power of negative x end exponent close parentheses

    • This can be pronounced "cosh"
  • Hyperbolic tangent

tanh x equals fraction numerator sinh x over denominator cosh x end fraction equals fraction numerator straight e to the power of 2 x end exponent minus 1 over denominator straight e to the power of 2 x end exponent plus 1 end fraction

    • This can be pronounced "than" or "tanch"

What are the graphs of the hyperbolic functions and their key features?

  • space y equals sinh x
    • Domain: x element of straight real numbers
    • Range: space y element of straight real numbers
    • Non-stationary point of inflection at (0, 0)
    • Its shape is similar to the graph of space y equals x cubed

edexcel-al-fm-cp-4-1-1-sinhx-graph

  • space y equals cosh x
    • Domain: x element of straight real numbers
    • Range: space y greater or equal than 1
    • Global minimum point at (0, 1)
    • Its shape is similar to the graph of space y equals x squared

edexcel-al-fm-cp-4-1-1-coshx-graph

  • space y equals tanh x
    • Domain: x element of straight real numbers
    • Range: negative 1 less than y less than 1
    • Non-stationary point of inflection at (0, 0)
    • Asymptotes at y=1 and y=-1
    • Its shape is similar to the graph of space y equals arctan x

edexcel-al-fm-cp-4-1-1-tanhx-graph

What other features of the hyperbolic functions and graphs do I need to know?

  • The graphs of y=sinhx and y=tanhx have rotational symmetry about the origin
    • This means that
      • sinh left parenthesis negative x right parenthesis equals negative sinh x
      • tanh left parenthesis negative x right parenthesis equals negative tanh x
    • sinh x and  are therefore odd functions
  • The graph of y=coshx is symmetrical in the y-axis
    • This means that
      • cosh left parenthesis negative x right parenthesis equals cosh x
    • cosh x is therefore an even function

What may I be asked to do with hyperbolic functions and their graphs?

  • Sketch graphs and transformations
    • e.g. space y equals sinh left parenthesis 2 x right parenthesis minus 4
      • Write as a transformation of y equals sinh xand apply the transformations in the correct order
    • Where possible label the key features of the transformed graph
      • Intersections with the coordinate axes
      • Equations of any asymptotes
      • Coordinates of any turning points
  • Find exact values
    • e.g. Find the exact value of sinh left parenthesis ln left parenthesis 5 right parenthesis right parenthesis
      • Use the definitions to write in terms of e
      • Use straight e to the power of ln k end exponent equals k and straight e to the power of negative ln k end exponent equals 1 over k

Examiner Tip

  • When using a calculator make sure you use sinh, cosh and tanh and NOT sin, cos and tan
  • Questions asking for values in exact form are often easier “to see” without a calculator, using the definitions of sinh and cosh, rather than trying to type in a complicated expression with e and ln

Worked example

a)
Find the exact values of
(i)
2 cosh left parenthesis ln left parenthesis 8 right parenthesis right parenthesis minus 3 sinh left parenthesis 2 ln left parenthesis 2 right parenthesis right parenthesis
(ii)
3 minus tanh left parenthesis 2 ln left parenthesis 3 right parenthesis right parenthesis plus tanh stretchy left parenthesis negative 2 ln left parenthesis 3 right parenthesis right parenthesis

al-fm-4-1-1-we-solution-a

 

b)
Sketch the graph of y equals 3 cosh open parentheses 1 fourth x close parentheses minus 1, labelling any points where the graph crosses the coordinate axes and any turning points.

al-fm-4-1-1-we-solution-b

 

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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.