Texas Instruments Titanium TI-89, User Manual

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Symbolic Manipulation 223
Symbolic Manipulation
Using Undefined or Defined Variables
When performing algebraic or calculus operations, it is important that you understand
the effect of using undefined and defined variables. Otherwise, you may get a number
for a result instead of the algebraic expression that you anticipated.
How Undefined and Defined Variables Are Treated
When you enter an expression that contains a variable, the TI-89 Titanium treats the
variable in one of two ways.
To see why this is important, suppose you want to find the first derivative of x
3
with
respect to x.
• If the variable is undefined, it is treated as
an algebraic symbol.
• If the variable is defined (even if defined
as 0), its value replaces the variable.
• If x is undefined, the result is in the form
you probably expected.