Guess the Function.

From the graph menu go to grid form and select square.
From the graph menu choose plot new function. A keypad will appear on screen. Press 2 x + 5. Then press okay. The function will appear.
By placing the cursor over the dot at the origin and holding down the left mouse button it is possible to reposition the graph.
Choose the selection arrow from the toolbox. Left click on the expression f(x)=2x +5
From the display menu choose hide function.
Select the point tool from the toolbox. Place the cursor over the graph line. When it turns blue, click the left hand mouse button to place a point.
Choose selection arrow from the toolbox.
With the point still selected go to measure and select abscissa, click on a blank region, reselect point and choose ordinate from the measure menu.
Click in a blank region. Click firstly on the x and then on the y values. Select tabulate from the graph menu.
Select the original graph line and choose display, line width, thick.
Plot the first guess by choosing Plot new function from the graph menu., this will appear as g(x).
To edit the function, double click on the expression, use the delete key on the computer’s keypad to delete the current entry and then enter the new function. / A graph is presented to pupils together with a table of values. Pupils guess the function by examining the graph and/or by checking values from the table. Their guess for the function can be checked by plotting in Sketchpad to see if it coincides with the given graph.
Plotting a graph
1.  The axes for a graph can either have the same scale or independent scales. Choose whichever is appropriate for the function. For this first function we will use ‘square’ i.e. the same scale.
2.  Plot the function y = 2x + 5.


3.  Hide the function expression.
Create a table of values
4.  Place a point on the line.
5.  Measure the abscissa and ordinate separately.
6.  Select the (x) abscissa and then the (y) ordinate measurements, create a table of values.
7.  When the table appears, there is a single line of entries. Double left mouse click in the table to enter those values into the table.
8.  Move the point to a new position on the line graph and double left mouse click in the table to enter the new data.
9.  Repeat as many times as required.
Guess the function
10.  When pupils have suggested a function, plot it. It’s a good idea to make the target line thick or a different colour.
11.  To plot a second pupil guess, sometimes it’s useful to plot a new function again and sometimes it’s appropriate to edit the first guess.
12.  Series of progressively more difficult functions can be set up in advance, with or without tables of values ready created. Sketchpad will plot polynomials and trigonometric functions. On the Sketchpad screen keyboard a quadratic has to be keyed in as x^2 although when it reproduces it as f(x) it appears as x².