Drawing Graphs from Tables (Edexcel IGCSE Maths A (Modular))

Drawing Graphs Using a Table

How do I draw a graph using a table of values?

• To create a table of values

  • substitute different x-values into the equation

    • This gives the y-values

• To plot the points

  • use the x  and y-values to mark crosses on the grid at the coordinates (x , y )

    • Each point is expected to be plotted to an accuracy within half of the smallest square on the grid

• Draw a single smooth freehand curve 

  • Go through all the plotted points

  • Make it the shape you would expect

    • For example, quadratic curves have a vertical line of symmetry

  • Do not use a ruler for curves!

Which numbers should I be careful with?

• For quadratic graphs, be careful substituting in negative numbers 

  • Always put brackets around negative values and use BIDMAS

    • For example, substitute x = -3 into y = -x² + 8x 

    • This becomes y = -(-3)² + 8(-3)

    • which simplifies to -9 - 24

    • so y = - 33

• For reciprocal graphs like , or , do not include x = 0

  • You cannot divide by zero

    • You get an error on your calculator

  • There is no value at x = 0 

    • The L-shaped branches can't cross the y-axis

    • There will be a vertical asymptote at x = 0

  • An example is given below with

• You should also be careful when there is a combination of different types of function

  • E.g. has a quadratic term and a reciprocal term

  • This makes it harder to know the shape of the graph

  • But you can still use a table of values to plot them

  • Just be aware of points like x = 0 as described above, where there will be no value

How do I use the table function on my calculator?

• Calculators can create tables of values for you

• Find the table function

  • Type in the graph equation (called the function, f(x)) 

    • Use the alpha button then X or x

    • Press = when finished

  • If you are asked for another function, g(x), press = to ignore it

• Enter the start value

  • The first x-value in the table

  • Press =

• Enter the end value

  • The last x-value in the table

• Enter the step size

  • How big the steps (gaps) are from one x-value to the next

  • Press =

• Then scroll up and down to see all the y-values