Texas Instruments TITANIUM TI-89 - Manual (Page 254)

Symbolic Manipulation 254
Note: Enter ln(x † y) instead of ln(xy) ; otherwise, xy is interpreted as a single variable
named xy.
Note: For ‚ or , press 8 Ã or 8 Â. You can also use 2 I 8 or 2 G
2 to
select them from a menu.
Using Substitutions vs. Defining a Variable Using Substitutions vs. Defining a Variable Using Substitutions vs. Defining a Variable Using Substitutions vs. Defining a Variable
However, substitution is preferable for most cases because the variable is defined only
for the current calculation and does not accidentally affect later calculations.
Because sin
L1
(sin( q )) = q is not always valid, the
expression is not simplified.
With a constraint, the expression can be simplified.
In many cases, you can achieve the same
effect as a substitution by defining the
variable.
Substituting x=1 does not affect the next
calculation.