Examples of what pupils should know and be able to do
Plot the graphs of simple linear functions, e.g. y = 2x – 3 or y = 5 – 4x, using all four quadrants, by generating coordinate pairs or a table of values.
Recognise that a graph of the form y = mx + c corresponds to a straight line and represents an infinite set of points.
Probing questions
How do you go about finding a set of coordinates for a straight-line graph, for example y = 2x + 4?
How do you decide on the range of numbers to put on the x and y axes?
How do you decide on the scale you are going to use?
If you increase/decrease the value of m, what effect does this have on the graph? What about changes to c?
What have you noticed about the graphs of functions of the form y = mx + c? What are the similarities and differences?
What if pupils find this a barrier?
See Step 5.
It may help pupils to see and use the links between equations in words,
plotted graphs and tables of coordinates. See Teaching
mental mathematics from Level 5: algebra p. 21: matching activities - Acrobat pdf document (36Kb).
Difficulties may also arise in:
- manipulation of positive and negative numbers;
- 'reading' the equation and understanding what it means.
If necessary refer to Step 6 in Properties of Number, Integers, Powers and Roots or Step 6 in Equations, Formulae and Identities.
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