Texas Instruments TI-92 Getting Started page 12

The TI-92 can graph piecewise-defined functions by using the "when" function. The "when" function is not on any
of the keys but can be found in the CATALOG or typed from the keyboard. The format of the when( function is
when(condition, trueResult, falseResult, unknownResult) where the falseResult and unknownResult are
optional arguments.
For example, to graph the function f (x) =
and graph x – 1 when the condition is false. First, clear any existing functions in the Y= screen. Then move to the y1
line and press W H E N (X 2nd < 0, X ∧ 2 + 1 , X – 1) ENTER (Figure 5.28). Then press
the graph. Figure 5.29 shows this graph in a viewing rectangle from –5 to 5 in both directions. This was done in Dot
style, since the TI-92 will (incorrectly) connect the two sides of the graph at x = 0 if the function is graphed in Line
style.
Figure 5.28: Piecewise-defined function
Other test functions, such as ≤, ≥ and ≠ as well as logic operators can be found on the Test sub-menu of the 2nd
MATH menu.
5.2.4 Graphing a Circle: Here is a useful technique for graphs that are not functions but can be "split" into a top
part and a bottom part, or into multiple parts. Suppose you wish to graph the circle of radius 6 whose equation is x
2
y = 36. First solve for y and get an equation for the top semicircle, y =
− −
2
36 x . Then graph the two semicircles simultaneously.
Use the following keystrokes to draw this circle's graph. First clear any existing functions on the Y= screen. Enter
− −
2
36 x as y1 and 36 x
– X ∧ 2) ENTER. Then press
Figure 5.30: Two semicircles
− −
Instead of entering 36 x
try this by going into the Y= screen and pressing
ENTER (Figure 5.32). The graph should be as before.
1 2
Graphing Technology Guide: TI-92

+
2
x 2,

−
x 1,

−
2
as y2 (see Figure 5.30) by pressing 2nd
GRAPH to draw them both (Figure 5.31).
2
as y2, you could have entered –y1 as y2 and saved some keystrokes. On the TI-92,
to move the cursor up to y2. Then press CLEAR (-) Y 1 (X)
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<
x 0
, you want to graph x
≥
x 0
Figure 5.29: Piecewise-defined graph
−
36 x
36 – X ∧ 2) ENTER (-) 2nd
Figure 5.31: Circle's graph – standard WINDOW
2
+ 2 when the condition x < 0 is true
GRAPH to display
2
, and for the bottom semicircle, y =
2
+
36