Taking it further

In the main problem you arranged four functions in a \(2 \times 2\) square according to two properties that the functions did or did not have. Now we will think about arranging eight functions in a \(2 \times 2 \times 2\) ‘cube’ based on whether or not the functions have three properties.

For example, can you complete this function cube for the following properties?

  • Where the function is well defined, two different input values give two different output values
  • The graph of function has asymptotes
  • The graph of function has rotational symmetry about \((0,0)\)
2 by 2 by 2 cube with 4 functions drawn on; The functions x + (1 over x) and x cubed minus x are drawn on adjacent cells and the functions x + 1 and 1 over (x + 1) on the opposite cells respectively

There are many ways to represent a cube and if you wanted to use the functions cards, you might find it simpler to arrange them in a \(4 \times 2\) table, i.e. two ‘layers’ of four functions.

For example, the table below could represent a function cube for the properties

  • The graph passes through \((0,0)\)
  • The graph is straight
  • The \(y\)-axis is a line of symmetry for the graph
Graph passes through \((0,0)\)
Graph is straight
\(y\)-axis is a line of symmetry
\[f(x)= \cdots\]

Graph passes through \((0,0)\)
Graph is straight
\(y\)-axis is not a line of symmetry
\[f(x)= \cdots\]

Graph passes through \((0,0)\)
Graph is not straight
\(y\)-axis is a line of symmetry
\[f(x)= \cdots\]

Graph passes through \((0,0)\)
Graph is not straight
\(y\)-axis is not a line of symmetry
\[f(x)= \cdots\]

Graph does not pass through \((0,0)\)
Graph is straight
\(y\)-axis is a line of symmetry
\[f(x)= \cdots\]

Graph does not pass through \((0,0)\)
Graph is straight
\(y\)-axis is not a line of symmetry
\[f(x)= \cdots\]

Graph does not pass through \((0,0)\)
Graph is not straight
\(y\)-axis is a line of symmetry
\[f(x)= \cdots\]

Graph does not pass through \((0,0)\)
Graph is not straight
\(y\)-axis is not a line of symmetry
\[f(x)= \cdots\]

Try to complete this function cube or make a different one.

You might need to make some extra function cards.

Make a note of any cells that you can’t think of functions for.

Make a note of properties that are difficult to combine in a function cube.