Graphing on the TI-83

Note that the TI-83 and the TI-83 plus have slightly different keys. This page uses the keys associated with the TI-83. The differences are that the TI-83 key is replaced by the TI-83 Plus key, and the TI-83 key is replaced by the TI-83 Plus key.

Example 4 in the textbook contains a TI-86 solution. The problem is to evaluate

11x⁵ + 12x⁴ - 10x³ +6x² + 15 for x=1.5 The solution given uses the evalF function on the TI-86 calculator. This is a good solution, if you have a TI-86. However, there is no evalF function on the TI-83 calculator. Therefore, we will look at the more general solution of assigning a value to the variable x and then entering the expression.

Figure 1 We start by assigning the value 1.5 to X. Then we can compose our expression 11x⁵ + 12x⁴ - 10x³ +6x² + 15 as 11X^5+12X^4–10X^3+6X²+15 after which we press the key to complete the line. The calculator computes the result as 139.03125, as shown in Figure 1.
Figure 2 We can ask the calculator to re-compute the answer, and to try to give the answer as a fraction. We do this by pressing to recall the previous expression, and then to open the MATH menu, where we select the operation by pressing the key. Having composed the new command, we press to execute that command, producing the fraction 4449/32. This is the answer in improper fractional form.

The TI-83 does not provide a command to change an improper fraction to a mixed number. However, we could write a small program to do this. The calculator used here actually does have such a program, called mixednum in it. The listing of that program is

The program is available for download at mixednum.83p. This program tries to convert the values stored in ANS to a mixed number. mixednum then displays the whole and fractional parts of the mixed number. Finally, mixednum redisplays the original value. It does this so that the value of ANS is exactly what it was before the program was run. The following screens will demonstrate how to run this program.

Figure 3	To find the MIXEDNUM program we open the program menu by pressing the key. This menu will list all of the names of all of the programs stored on the particular calculator. The calculator used to generate the figures on this page happens to have many programs on it. The programs are listed in alphabetic order. MIXEDNUM does not appear in Figure 3. Therefore, we can press the key to move the highlight down the list until we have found the MIXEDNUM program.
Figure 4	In Figure 4 we have moved the cursor down to the MIXEDNUM program. We actually select the program by pressing the key.
Figure 5	Having selected the MIXEDNUM program in Figure 4 means that the calculator has displayed the command prgmMIXEDNUM on the screen. We still need to tell the calculator to perform the program. We do this by pressing the key again.
Figure 6	Figure 6 shows the results, the output, of the MIXEDNUM program. In particular, using the value of ANS, the program determined that 139.03125 can be expressed as the mixed number 139 1 / 32 MIXEDNUM then redisplays the original value so that ANS is returned to hold 139.03125.

Figure 1	We start by assigning the value 1.5 to X. Then we can compose our expression 11x⁵ + 12x⁴ - 10x³ +6x² + 15 as 11X^5+12X^4–10X^3+6X²+15 after which we press the key to complete the line. The calculator computes the result as 139.03125, as shown in Figure 1.
Figure 2	We can ask the calculator to re-compute the answer, and to try to give the answer as a fraction. We do this by pressing to recall the previous expression, and then to open the MATH menu, where we select the operation by pressing the key. Having composed the new command, we press to execute that command, producing the fraction 4449/32. This is the answer in improper fractional form.