TI89 MiniTutorial

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TI-89 Mini-Tutorial

• Piecewise Functions

The purpose of the mini-tutorials is to
demonstrate the capabilities of the TI-89s
built-in computer algebra system (CAS). This
presentation in particular focuses on defining
piecewise functions.
Before you start this tutorial, you should
execute the NewProb command under the Clean Up
tab to clear a through z, turn off all graphs,
and clear your Home screen.
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Unfortunately, defining piecewise functions in
the TI-89 isnt very convenient. It actually
takes a little bit of programming logic to
understand how the definitions work, but
hopefully the steps outlined here will help those
who have never taken any programming.

• The when( ) command is what we will need to
  create any piecewise-defined function, so lets
  first look at how it works. We will be using its
  two required and first optional arguments for our
  purposes
• Condition the expression to be tested.
• True result the result when the condition is
  true.
• False result (optional) the result when the
  condition is false.

In our definitions, the condition will be the
domain of the first piece of our function, the
true result will be the first piece of the
function, and the false result will be the second
piece of the function.
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For those that have not had any programming
experience, that last slide probably didnt make
too much sense. Lets try using an example as a
different approach to explaining it.
condition
when( condition, true result, false result )
true result
false result
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The when( ) command can only be found in the
Catalog (pressing CATALOG, . will go right to
it), but you can always type it in also.

• The various inequality and equality symbols can
  be found in the Math menu (press 2nd, 5)
  under the 8Test dropdown menu. There are also
  keyboard shortcuts
• 2nd, 0 and 2nd, . for lt and gt.
• ?, 0 and ?, . for ? and ?.
• ?, for ?.

For compound inequalities, you have to use and
or or. For example, the domain 0 lt x ? 2 would
be entered as xgt0 and x?2. Its usually
quickest to type and and or using the
alphabet keys versus calling the operators from
the Math menu.
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The when( ) command can be nested in itself when
you have more than two pieces in the function.
Heres how

• Enter the condition and true result as before
  for the first piece of the function.
• For the false result, start a new when( )
  command.
• The second when( )s condition and true result
  need to be the second piece of the function.
• The last false result would be the last piece
  of the function.

would be defined as when(xlt0, x-1, when(x?0 and
x?2, x2, 3-x) )
would be defined as when(xlt0, x-1, when(x?0 and
x?2, x2, 3-x) )
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TI-89 Mini-Tutorial

• Piecewise Functions

This concludes the presentation on defining
piecewise functions.
Details and additional information can be found
in the TI-89 manual. Click here to download a
PDF version of it.