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TI-89 Calculator and Systems Of Linear Equations

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

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  1. SCO

    SCO Guest

    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

    press up arrow... select your previous answer (a+bi)/(c+di) and press
  3. SCO

    SCO Guest

    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

    (results courtest of Mathcad).

    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. 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 who

    Guess who Guest

    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

    Doh!! <Head Slap>

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

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

    Steve O.
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