Using Undefined Or Defined Variables - Texas Instruments TI-89 Titanium User Manual

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.
• 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.
To see why this is important, suppose you want to find the first derivative of x
respect to x.
• If x is undefined, the result is in the form
you probably expected.
Symbolic Manipulation
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