Section 1-2 "Variables and Expressions"

Technology objective: After discussion, have students will review how to store a number in the TI-34 and learn how to store numbers in the TI-81.

Lesson: Put a = 45 on board. Then write the following:

a - 8

a * 3

a / 3

a + 100

Have the students to perform the problems manually. Then ask how they could use the store function on the TI-34 calculator to perform the above problems. Review how to store a number in the TI-34 calculator by having the students go back to their "lab" sheets. Then try the following by storing the number first. (Remind the students to use the CE/C key.) If a = 3.2, then find the following:

a - 2

a / .5

a * .2

a + 37.5

TI-81 information

Students can store number or numbers in the TI-81. What is great about this is they will store the numbers using any variable. Therefore, they will be reinforcing what they are learning.

To store a number in the TI-81 calculator:

1. Enter the number you want to store. For example, 6.

2. Now press the store key - (STO).

3. Finally, choose the variable you want to store that number as. In this case, lets say "a". To do this you will have to press ALPHA first to access the letters and then select any of the letters in gray.

Now show the class the following problem:

a + 7

Have them enter the expression in their calculator exactly as it appears. The answer should show up after you press enter.

Now have the class think about the following problem:


Have them guess what this means, does it mean the answer will be 26? Is there an operation? Now have them put that expression in their calculator to see what they get. After they get the answer, have them write down in their journals what they think 2a means. Have them predict what they think the following mean. After they make predictions, have them verify their results by entering those same expressions in the calculator.

Try) 3a




13a - 5

100a + 7

Ask the class what they think the answer to the following problem is:

If a = 6 and b = 2, what is a + b?

They should already know the answer. However, let them check using the calculator to see if the calculator is right. What is wonderful about the TI-81 calculator is that they can store more than one variable. Have them store the number 2 in the TI-81 as the letter "b". Then enter "a + b." The answer should be the same as what they calculated.

Now have the students first predict the answers to the following and then perform the same calculations by using the calculator.

a + b - 2

3a - 2b

5a + 12b

a/2 + 3


(Game) - "Evaluate the expression"

Students will sit in rows, their team being their row. In this game, students will evaluate an expression by substituting a value in for their variable. Their answer will then be passed back to the person sitting behind them who will enter that value for the variable in their expression. This will continue until the last person substitutes the value in his variable. He will then raise his hand and show his answer to the judge. (The answers will have to be calculated before hand) If it is wrong the row will have to start all over again to figure out where the mistakes occurred. This game can be played as a race or every team that gets the same final results gets a point.