Test; Zoom In - Texas Instruments TI-82 Keystroke Manual

page 103

24 Test

The items on the TEST menu may be used to tell whether a relationship between two numbers or
expressions is true or false. To see how it works, let's let the calculator verify something you
already know: 7 is less than 8. At the Home screen type a 7 and then press 2nd [TEST] (the second
function on the MATH key) to produce the TEST menu. The "less than" symbol < is choice 5 on the
menu. Either press 5 or use the Down Arrow key to highlight the 5 and press ENTER. The <
symbol will appear on the Home screen after the 7. Then type an 8, so that the Home screen now
shows 7<8. You want to know if this statement is true. The calculator will tell you when you
press ENTER. The calculator will display a 1 if the statement is true or a 0 if the statement is false.
In this case, of course, the calculator displays a 1, since 7 is less than 8.
Now let's enter a false statement: 4 > 11. Type a 4 and then press 2nd [TEST] to produce the
TEST menu. The "greater than" symbol > is choice 3 on the menu, so press 3 to produce the >
symbol on the Home screen after the 4. Now type 11 and press ENTER. The calculator displays a
0 to tell you that the statement is false.
Next let's try one that perhaps isn't so obvious. Is
division key ÷ to produce the diagonal slash division sign /) and press ENTER to find out. The
statement is false, since the calculator responds with a 0.
The TEST menu may also be used to test proposed solutions of equations. For example, to test
whether 2 is a solution of the equation
Then type in the equation
menu.) Since the calculator displays the value 1 (true), 2 is a solution of the equation. Using the
same method, test whether –2 is a solution of the equation
the value of x and then type in the equation, the calculator should display the value 0 (false) when
you press ENTER, indicating that –2 is not a solution of the equation. Note: This approach to
testing solutions of equations is reliable only for exact solutions. Rounded solutions or other
approximate solutions usually do not test as correct.
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25 Zoom In

The Zoom In feature on the ZOOM key menu is used to get a closer look at some feature of a
graph. Before you use the Zoom In feature, there is one other matter of business to conduct: you
must determine how much the calculator will zoom in (or out). Press the ZOOM key and then press
the Right Arrow key to place the highlight on the MEMORY menu heading to display the MEMORY
menu. Press 4 to choose Set Factors....
− x = −
1 3 5
− x = −
and press ENTER. (Note that "=" is choice 1 on the TEST
1 3 5
>
5 59
? Type in 5/8 > 59/93 (using the
8 93
, first store 2 as the value of x. (See 14 Store.)
+ = −
2 x 5 1 x . After you store –2 as
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