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.

8. Guest

Thank you. I'll try this at home later.

Original poster, posting from an alternate e-mail address.

Steve O.