### Trinomial Factoring Program on the TI-83, version 2

The web page 208303.htm presents and describes a program that performs the "split the middle term" scheme for factoring trinomials of the form

Ax2 + Bx + C
Note that we are assuming that A, B, and C are integers, and that neither A nor C is 0. As noted at the end of that page, the output of the program is correct, but difficult to read. This page presents a listing of a new version of that program, one that produces nice looking output. In order to acheive this nicer looking output, the new program, TRIFACT2, actually uses another program, TOSTR, which must be available on the calculator. The listings below are for the TI-83 version of the TRIFACT2 program, given in three parts, and for the TOSTR program, given in one part. The TRIFACT2 listing has been modified with the tracing lines on the left to help you identify the ranges of the the IF-THEN and IF-THEN-ELSE constructs in the program, along with the FOR structure.
 TRIFACT2, part 1 TRIFACT2, part 2
 TRIFACT2, part 3 TOSTR

A comparison of part 2 of the TRIFACT2 program with the TRIFACT1 program given on the earlier page, should confirm that the main part of the program is unchanged from one version to the other. The extra lines in version 2 are used to format the output of the program so that it looks nicer. Also, notice that the TRIFACT2 program calls (makes reference to) the TOSTR program in a number of places.

Naturally, one could enter the programs into a calculator. However, the TI-83 file for TRIFACT2 in is available at trifact2.83p and the TI-83 file for TOSTR at tostr.83p. Depending upon your browser, you should be able to save the file to your disk and then transfer it via TI-Graphlink, assuming you have the program and the required cable.

We conclude this page with few sample runs of the TI-83 version of the TRIFACT2 program:
 Figure 1 We open the PRGM menu by pressing the key and then moving, if need be, to find the TRIFACT2 program. Having highlighted the TRIFACT2 program, we can press the key to move to Figure 2. Figure 2 All that has been accomplished is to paste the command prgmTRIFACT2 onto the screen. We will have to press the key to actually start to run the program. Figure 3 In Figure 3 the program has started. It has cleared the display and written the heading, FACTOR AX2+BX+C at the top. In addition, the calculator has asked for, and we have supplied, values for the coefficients A, B, and C. We have entered the value 1 for A, 11 for B and the value 24 for C. These are the coefficients for X2 + 11X + 24 The calculator is waiting for us to press to accept the value for C and to move on with the program. Figure 4 Figure 4 shows output from the calculator. It writes the word FACTOR followed, on the next line, by a restatement of the problem, followed by the two factors: (X+8)(X+3) Figure 5 The program was completed in Figure 4. To restart it, we press . Figure 5 gives the data entry for the problem 20X2 + 13X - 21 Note the negative value for C, namely, -21. Figure 6 To accept our final value and continue the program we press . Figure 6 gives the result, namely a restatement of the problem, followed by the two factors: (5X+7)(4X-3)

PRECALCULUS: College Algebra and Trigonometry
© 2000 Dennis Bila, James Egan, Roger Palay