Stretches (CIE A Level Maths: Pure 1)

Revision Note

Test yourself
Roger

Author

Roger

Last updated

Did this video help you?

Stretches

What are graph transformations?

  • When you alter a function in certain ways, the effects on the graph of the function can be described by geometrical transformations
  • With a stretch all the points on the graph are moved towards or away from either the x or the y axis by a constant scale factor

 

Stretches What Is, A Level & AS Level Pure Maths Revision Notes

What do I need to know about graph stretches?

  • The graph of y = af(x) is a vertical stretch of the graph y = f(x) by a scale factor of a, centred on the x axis
    • The x coordinates of points stay the same; y coordinates are multiplied by a
    • Points on the x axis stay where they are
    • All other points move parallel to the y axis, away from (a > 1) or towards (0 < a < 1) the x axis

     Stretches statement_vert_Illustration, A Level & AS Level Pure Maths Revision Notes 

  • The graph of y = f(ax) is a horizontal stretch of the graph y = f(x) by a scale factor of bold 1 over bold italic a, centred on the y
    • The y coordinates of points stay the same; x coordinates are multiplied by bold 1 over bold italic a
    • Points on the y axis stay where they are
    • All other points move parallel to the x axis, away from (0 < a < 1) or towards (a > 1) the y axis

     Stretches statement_horiz_Illustration, A Level & AS Level Pure Maths Revision Notes

  • Any asymptotes of f(x) are also affected by the stretch (stretch them as you would stretch the function of a straight line)
  • If an asymptote is one of the coordinate axes, or is parallel to the direction of the stretch, however, it will not be affected

Stretches Asymptotes_Illustration, A Level & AS Level Pure Maths Revision Notes

Examiner Tip

  • When you sketch a stretched graph, be sure to indicate the new coordinates of any points that are marked on the original graph.
  • Try to indicate the coordinates of points where the stretched graph intersects the coordinate axes (if you don't have the equation of the original function this may not be possible).
  • If the graph has asymptotes, don't forget to sketch the asymptotes of the stretched graph as well.

Worked example

Stretches Example, A Level & AS Level Pure Maths Revision Notes

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Roger

Author: Roger

Expertise: Maths

Roger's teaching experience stretches all the way back to 1992, and in that time he has taught students at all levels between Year 7 and university undergraduate. Having conducted and published postgraduate research into the mathematical theory behind quantum computing, he is more than confident in dealing with mathematics at any level the exam boards might throw at you.