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Math Help - Storing Formulae

  1. #1
    Senior Member DivideBy0's Avatar
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    Storing Formulae

    Do you think it would be a good idea to store complicated and/or important formulas such as the root-finding ones?
    What I essentially mean is that you type the formula in then store it, then type something like insert x=1 into the formula.
    (I have a TI-89)
    How would I go about doing this?

    Thanks
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by DivideBy0 View Post
    Do you think it would be a good idea to store complicated and/or important formulas such as the root-finding ones?
    What I essentially mean is that you type the formula in then store it, then type something like insert x=1 into the formula.
    (I have a TI-89)
    How would I go about doing this?

    Thanks
    It depends on three things:
    1) What kind of work you tend to do and
    2) How complicated the formula is and
    3) How you are storing the formula.

    1) If you are ceaslessly doing the same calculation over and over again, of course it makes sense. Everybody I know does this. However, if you are in school and you simply want to store a way to solve quadratic equations for you then I would recommend that you don't. The purpose of schoolwork is practice. Writing a program to solve the problems for you is good a exercise, but defeats the purpose of the homework.

    2) If you have a simple formula for what you need then you can simply store it as a formula. For example if you are finding many points on the function sqrt{x^3 + 3x^2} + exp{sin(5x + 4)/x!} then, yeah, I'd write out the function on the screen and automate it. You should be able to copy and paste the line above and put a "|x = 3" (for example) after each line to evaluate it at a specific x value.

    3) For a genuinely complicated formula you can go into the editor mode and define either a function or write a program to do it for you. For example if you are trying to find the exact solutions of a quartic polynomial, a simple process like I described in 2) is going to be impossible. But you can write a program to do it if you have the formula handy.

    Unfortunately I have a TI-83 and a TI-92, not a TI-89. The 89 is similar to the 92 but I don't know how close the details are, so I can't help you with the specifics.

    -Dan
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  3. #3
    Senior Member DivideBy0's Avatar
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    Thanks, I didn't know you could simply use |x=n to substitute in...
    I also just discovered a few other things with it. I think it's a great, convenient thing to do!
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  4. #4
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    Quote Originally Posted by DivideBy0 View Post
    Thanks, I didn't know you could simply use |x=n to substitute in...
    I also just discovered a few other things with it. I think it's a great, convenient thing to do!
    Hello,

    one additional remark:

    If you store the (for instance topsquark's) term sqrt(x^3 + 3x^2) + exp(sin(5x + 4)/x!) into y1(x) then you can get the value of this term for x = 3 by typing y1(3) [Enter]. That means your TI89 is calculating the y-value of a function.

    EB
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  5. #5
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    Quote Originally Posted by topsquark View Post
    Unfortunately I have a TI-83 and a TI-92, not a TI-89. The 89 is similar to the 92 but I don't know how close the details are, so I can't help you with the specifics.

    AFAIK, the 89 is the 92 minus the qwerty keyboard and a bit of speed.
    And an invaluable tip to all 89 users: there are copy and paste buttons (the yellow diamond and two other top-row, left-side keys) that you can use to copy functions off the upper part of the home screen and into the y= editor. You can also highlight text similar to computers by pressing and holding either the yellow diamond or alpha key (don't remember which) and using the arrows if you want to copy stuff from the entry area.
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