*General: *
To type an upper case letter, press ALPHA key, followed by the letter.
To type a lower case letter, press 2nd key, then ALPHA key, followed by the
letter.
To enter the program into the calculator, press PRGM, then F2 (which selects
the EDIT box), then the program name (e.g. SLOPE) followed by ENTER. The
calculator will shift to a new line and display the colon : which must
start each instruction. After typing each instruction, press the ENTER key.
When navigating menus, use EXIT to go back.

This program is more elaborate than the others because it must link the
computational and graphing operations of the calculator.

COMMAND: Explanation and keying instructions::FnOff Inactivates function graphing. GRAPH, F1,MORE,MORE,F2. :ClDrw Clears the screen. GRAPH,MORE,F2,MORE,F4. :Prompt xMin,xMax,yMin, yMax Prompts for input of screen parameters. Prompt is F3,F2. xMin, etc. are on the GRAPH,F2 menu. :7(xMax - xMin)/83->H Calculates horizontal step-size. - is to the right of 6, / is the division key, which is under the ^ key, -> is STO. :7(yMax - yMin)/55->K Calculates vertical step-size. :1/(0.4H)^2->A The numbers A and B are used in calculating :1/(0.4K)^2->B the how long the lines should be. :xMin+0.5H->x Calculates position of lower left-hand slope line. :yMin+0.5K->Z Use x-VAR to get x. :1->I Initialize I: counts columns. :Lbl P Labels this program location. Lbl is F4,MORE,F4 :1->J Initialize J: counts rows. :Z->y Initialize y for the current column. Use lower case y if you use l.c. y in the expression y1. :Lbl Q Labels this program location. :y1->T Program applies expression stored as y1 to compute the current slope. To get y1, type y and then 1. :1/sqrt(A+B*T^2)->C sqrt is the square-root (2nd x-squared, to the left of 7). * is the times key (next to 9). These :T*C->S two instructions calculate the horizontal and vertical extent of the line segment to be drawn. :x->U Store current x,y values as U and V. :y->V :Line(U-C,V-S,U+C,V+S) Draws a line segment through (x,y). The comma is the key to the left of the 4 key. :V+K->y Increment y. :IS>(J,8) Add 1 to J and test. If less than or equal 8, go to the next instruction (i.e. proceed up the column). If greater, skip next instruction. For IS>(, press F4 (chooses CTL menu), MORE, MORE, F1. :Goto Q :U+H->x Increment x (i.e. move to next column). :IS>(I,12) Test if all columns are done. :Goto P

*Running the program:* First enter the function giving the slope:
Press GRAPH, F1, then type it in as a function of the two variables
x (use x-VAR) and y (use same case (upper/lower) as in program. (e.g. x+y).
Then EXIT,EXIT to return to home screen.
Now PRGM, F1, then the F-key under the word SLOPE in the
screen, then ENTER. Enter numbers at the question mark (?) prompts.
After graph is drawn, to exit press EXIT key.

*Check:* For y1 = -x/y get circles centered at the origin. The
circles will be round if your screen parameters have the correct aspect ratio.

*Check:* For y1 = x+y and window [-3,3]x[-2,2], calculator screen
should have the image shown on the right. (Image generated with a
SHARP EL-9300C; TI-85 has finer resolution.)

Math Dept SUNY Stony Brook

tony@math.sunysb.edu

September 12 1997