Calculator User Manual

Chapter 15: Equation Solving
205
15EQSOLV.DOC TI-86, Chap 15, US English Bob Fedorisko Revised: 02/13/01 2:34 PM Printed: 02/13/01 3:04 PM Page 205 of 1215EQSOLV.DOC TI-86, Chap 15, US English Bob Fedorisko Revised: 02/13/01 2:34 PM Printed: 02/13/01 3:04 PM Page 205 of 12
The TI
-
86 solves equations through an iterative process. To control that process, you can
enter lower bounds and upper bounds that are close to the solution, and enter a guess
within those bounds in the prompt for the unknown variable.
Controlling the process with specific bounds and a guess helps the TI
-
86 in two ways.
♦
It finds a solution more quickly.
♦
It is more likely to find the solution you want when an equation has multiple solutions.
To set more precise bounds at the
bound=
prompt, the syntax is:
bound={
lowerBound
,
upperBound
}
At the prompt for the unknown variable, you may enter a guess or a list of two guesses. If
you do not enter a guess, the TI
-
86 uses (
lowerBound
+
upperBound
)
à
2 as a guess.
On the solver graph (page 207), you can guess a solution by moving the free-moving cursor
or trace cursor to a point on the graph between
lowerBound
and
upperBound
. To solve for
the unknown variable using the new guess, select
SOLVE
from the solver graph menu. The
solution is displayed on the interactive-solver editor.
Editing the Equation
To edit the equation stored to
eqn
when the interactive-solver editor is displayed, press
$
until the cursor is on the equation. The equation-entry editor is displayed. The TI
-
86
automatically stores the edited equation to
eqn
as you edit.
If you store an equation to
eqn
by recalling the contents of an equation variable, such as
y1
,
and then edit the equation stored to
eqn
, the original equation (in
y1
, for example) is not
changed. Likewise, subsequently editing the contents of the equation variable (
y1
, for
example) does not change
eqn
.
lowerBound
<
upperBound
must be true.
You can enter a list variable
at the
bound=
prompt if a
valid two-element list is
stored to it.
If you exit the equation
solver, any equation stored t
o
eqn is displayed when you
return to the equation solver.