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.
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.
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.
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.
Click in a blank
region. Click
firstly on the x
and then on the y
values. Select
tabulate from the
graph menu.
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.
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).
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.
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.
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.