Sharp EL-531RH Teachers Manual page 28

Function Tables
Return to the calculation for x = 5 and redo the calculation for the equation y = 4x - 3.
Add another line to the table and calculate the values of y for the new equation.
Plot the second graph with the first on the same axis.
What do you notice about the graphs and the numbers in the table?
What do you think will happen if you try another similar equation such as y = 4x - 1,
y = 4x + 1, or y = 4x + 4?
Can you explain the number pattern and the picture you have produced?
• • • • • • • • • • • Using the activity in the classroom • • • • • • • • • • •
This activity should be introduced after practicing substitution.
Start the activity as a whole class so the students can gain confidence in using the calculator and
see the advantages of calculating first and then recording the results to speed up the process of
making the graph table. The students can calculate the y values for the second equation themselves
and quickly continue with other suggested equations using multi-line playback to go directly from
the (x, y) values to the graph without needing to record the result in a table. This enables the
families of graphs to be compared rapidly. Try extending the activity by using graphs with different
gradients to establish the parallel nature of the graphs, and then try keeping the intercept constant
and varying the gradient.
• • • • • • • • • • • • • • • Points for students to discuss • • • • • • • • • • • • • •
The idea of using the playback function as a rapid way to calculate function values can be applied to
a wide range of equations including polynomials, trigonometric functions, etc. Students can do
calculations in one sequence and then use the playback function to go back through the answers
and record or plot them all at once.
Further Ideas
Investigations on graphs can be done more quickly if the playback function is used so each
function does not have to be retyped at every entry. Demonstrate this by using the following
suggestions:
• Solve a quadratic function such as ax
• Use the calculator to generate values of a trigonometric function and enter the results
directly onto a graph using the playback function.
2
+ bx + c = 0 for varying values of a, b, and c.
27
Junior high school