# TI-89 Calculator and Systems Of Linear Equations

Discussion in 'Electronic Basics' started by SCO, Sep 12, 2005.

1. ### SCOGuest

Well, I finally went out and bit the bullet. I purchased the TI-89
Titanium. I have to say that for the price I paid, I'm not wildly
impressed. The display is not at all vivid or strong, and the
keyboard is anything but intuitive.

However, I'm posting/griping about a particular issue. The calculator
comes with a particular program, a Simultaeneous equation solver,
which is precisely what I purchased it for. It's actually a pretty
good program, in terms of data entry, but it has one major
idiosyncracy (at least that I've found so far): When I put in
equations with complex coefficients, as often as not it reports
results with complex values in the denominators, along the lines of:

..345/(1.34 + 2.3j)

Sometimes the solution is even more complicated, in the form of

(a + bi)/(c+di)

It seems a no brainer to me that the calculator should automatically
do the work of clearing the complex value from the denominator, giving
me a nice, simple

1.234 + 5.678j

Does anyone know if there is a simple, one-button way to tell the
program to flush the complex numbers from the denominator, to give me
the simple result that I need?

Thanks in advance for all replies.

Steve O.

2. ### Guest

i dont know about 1 button way

but if you type in

(a + bi)/(c+di)

ti 89 is giving

g + ei

(which means it is actually simplifying)

so a quick fix would be to

enter

3. ### SCOGuest

Thanks for the suggestion, but no, not me for it's not. At least, not
when I am in that program (Simulateous Equation Solver). I press up
arrow to highlight the solution, and then press <enter>, but the
solution in the form of (a + bi)/(c + di) just "sits" there, without
reducing to g+ ei.

Worse yet, even in basic "command line" mode, typing an expression
like (2+i)/(2-3i) gives me

-.3333 * (i + 2) / (i - .666666)

when I should be seeing 0.077+0.615 i

I've also tried changing the Mode of the complex format from Real to
Rectangular to Polar, and as far as I can tell, that does nothing!!
Is there a bug in the software (gee, that would be a surprise....), or
am I missing a trick here.

Steve O.

4. ### Guest

that is very strange.

okay, one thing though, i was talking about TI 89 (not TI 89 Titanium,
although I heard both have the same capabilities, but the Titanium has
more flash ram or whatever)

in any case, i strongly believe it works.

tell me one thing... what happens when you press the diamond and press
enter, does it simplify then ? (in my TI 89, the diamond is a agreen
button, and when you press that and press "enter", that is same as ~=
...i.e. approximate)
try that and tell me what happens then

(but unfortunately though, when you do that, you'll lose the fractions
and get the exact values.. so for example 1/2 + 3/4i actually becomes
0.5 + 0.75i)

anyway, see what happens when you do that.

5. ### John O'FlahertyGuest

SCO, you are using a variable 'i' rather than the i of imaginary. You
get the imaginary i by pressing 2nd followed by the 'catalog' button.

6. ### Guest

AAAH... that could be it dude.
use the yellow "i" (it looks FATTER than an ordinary "i")

7. ### Guess whoGuest

Where you clearly typed in something incorrectly, or in the wrong
order, or through misunderstanding.
....when working to three decimal accuracy, and a sledgehammer to kill
a fly.

On the other hand, having had the practice, it takes only a few
*seconds* to calculate:

(2 + i)/(2 - 3i)
= [(2 + i)/(2 - 3i)]/[(2+3i)/(2+3i)]
=[4 - 3 + 8i] / [4 + 9]
=(1 + 8i)/13

....not so easy to type or see in ASCII, as it is to write it quickly
on the page.

This is done in high schools here, where students [OK, most] do
generate the skill prior to college entry, and learn useful terms such
as "difference of squares" and "complex conjugate" at the same time.