Texas Instruments PLUS TI-89 - Manual (Page 85)

68 Chapter 3: Symbolic Manipulation
03SYMBOL.DOC TI-89/TI-92 Plus: Symbolic Manipulation (English) Susan Gullord Revised: 02/23/01 10:52 AM Printed: 02/23/01 2:12 PM Page 68 of 24
¦ Substitution occurs only
where there is an exact
match for the substitution.
¦ Infinite recursions can occur when you define a substitution
variable in terms of itself.
sin(x)|x=x+1
When you enter a substitution that causes an infinite recursion:
−
An error message is
displayed.
−
When you press N, an
error is shown in the
history area.
¦ Internally, an expression is sorted according to the automatic
simplification rules. Therefore, products and sums may not match
the order in which you entered them.
−
As a general rule, you
should substitute for a
single variable.
−
Substituting for more
general expressions
(either
m ø c ñ =e
or c с ш m=e ) may not work
as you anticipate.
Be Aware of the
Limitations of
Substitutions
Tip: Use the solve function
to help determine the single-
variable substitution.
Only x 2 was replaced, not x 4 .
Define the substitution in
simpler terms for a more
complete substitution.
Substitutes sin(x+1), sin(x+1+1), sin(x+1+1+1), etc.
No match for substitution