Now please notice that the text you see on the TI-89 page — the text which introduces this post — is only “Yes, you can use photos.”

But when you open this post, you see all this text.

Now ain’t that cool?

And you can do the same.

By Donald Ingram, Sr. Prof.

The TI-89 Titanium calculator is the only calculator or software known to the author that can deliver correctly derived and converted units while solving for any unknown in an equation. When the user learns and collects a databank of these equations stored in an easily retrievable format and protected against loss with backup capability, the user will have gained a tool of great value which will serve the user and his/her employer well into the future.

The following calculator programming styles are intended to be a pattern to train the user in quick, correct, and advanced calculating capability, leading to greater personal worth in the job market.

On successfully mastering the material demonstrated in this paper, the user will be able to perform the following Objectives, arranged in progressively more powerful order:

1. Solve a numeric expression in HOME

2. Solve a unit expression in HOME

3. Algebraically solve an equation in HOME for any variable

4. Solve an equation or expression for any variable, with units

5. Establish a memory Folder and Variable (=file name) for storing useful equation solvers

6. Copy and Paste equation solvers to memory and to the command line

DIRECTIONS WITH EXAMPLES:

1. Solve a numeric expression in HOME

In this first objective, this calculator works like any inexpensive lesser calculator.

Ohm’s law states I=V/R current (I) is voltage (V) divided by resistance (R)

If the voltage is 12 V and the resistance is 300 ohms you may solve the function V/R like this

On the command line of HOME, enter 12÷300 and press ENTER.

You should see 40E-3 (ENGINEERING MODE) 40E-3 indicates 40 mA of current

or 4.E-2 (SCIENTIFIC MODE) indicates 40 mA of current

or .04 (NORMAL MODE) indicates 40 mA of current.

MODE Set the mode most useful to you by pressing MODE, cursor down to Exponential Format, right cursor, and up or down to select the mode you need. Then press ENTER, ENTER, ENTER. There are 3 pages of MODEs, accessible by pressing MODE, then F1, F2, or F3

I suggest ENGINEERING MODE for all electronics, as it produces 10 to powers of 3, corresponding to k kilo, M mega, G giga, T tera, P peta, and m milli, micro, n nano, p pico, f femto.

The powers of ten use the EE key. 33 micro is entered as 3, 3, EE, (-), 6; it is shown as

Here is one of the features that make this calculator so much better than a standard calculator: It remembers your operations and their results for as many as 99 problem-answer history pairs. You can come back to a problem you did 99 calculations ago (last week?, last month?) and review it or use it again, without re-entering the characters all over again. This saves time, reduces errors, helps your memory, improves accuracy (because you don’t need to round off), and helps you review how to do problems.

MEMORY You can set the history pairs to 99 by pressing F1, scrolling to 9:Format, ENTER, scroll to the right, then scroll down to 99, and ENTER. Thereafter, you will see some pair out of 99 in the lower right corner, like 21/99.

To re-use a previous problem or answer, scroll up to highlight it and press ENTER. It appears on the command line where the cursor was before you scrolled up.

2. Solve a unit expression in HOME

SECOND FUNCTION KEYS

All yellow characters are accessed with the diamond key,

all blue characters are accessed with the 2ND key,

all white characters are accessed with the ALPHA key.

Amperes = Volts / Ohms Now let the calculator verify it. Key in _v÷_ohm . (The underscore “_” is the diamond key followed by MODE.) You should get 1._A, or one ampere.

Similarly, key in _a x _ohm to get 1._v . Key in _v÷_a to get 1._ . You will notice the calculator substitutes the symbol for ohm. You can do it also. Later.

You notice that when you enter units in the expression, the calculator gives you the correct conversion. You can use this feature to detect expressions that are incorrect; they will give incorrect units.

3. Algebraically solve an equation in HOME for any variable

To clear the values from all single character variable names (a-z), press F6 (2ND F1), ENTER, ENTER.

Since I=V/R, press F2 (solve( ) ENTER, ALPHA I, =, ALPHA V, ÷ALPHA R, comma (,), ALPHA I, )

Now press ENTER.

If you did this correctly, the command line will read solve(i=v/r,i)

Verbally solve(i=v/r,i) reads “Solve the equation i=v/r for i.”

Now you can also solve for any other variable by simply placing your cursor to the right of the “i”, and backspace erase over it with the back arrow key (), and keying in the preferred variable.

Solve for v: solve(i=v/r,v) You should see the problem: and its solution:

solve(i=v/r,v) v=i•r

You can just as easily solve for r.

Here is a screen shot illustrating what we have learned:

You see a valuable resource tool illustrated here: the algebraic manipulation of any formula without making mistakes.

If we want to know just how much voltage vl appears across an inductance l when a change of current di occurs in the time span dt, we use the formula:

vl=l•di/dt

Or, to solve for l, di, or dt, we simply replace them after the comma in the solve( command:

Again, you see algebraic manipulation without mistakes.

CLEARING OF VARIABLES These variables must have no initial values to show algebraic manipulation this way. If necessary, we could clear vl, l, di, and dt with the command

This clears single and multiple character variables the same way as 2ND F1 (F6) clears single character variables. DelVar can be found by pressing CATALOG and d, then scrolling down through the catalog of all available commands to DelVar.

4. Numerically solve an expression in HOME with units

UNITS can be found by pressing 2ND UNITS, and scrolling down to the type of units, then to the right to the unit we need. For instance, for milliHenrys, we scroll down to the 3RD page of units to Inductance,

then to the right and down to _mH, and press ENTER, ENTER, ENTER. You can scroll a whole page at a time by pressing 2ND and the down cursor.

If we wanted to know the voltage required to push 2 amps in 3 seconds through a 12 millihenry inductor, we could enter the expression any of these ways:

12_mHx(2_a÷(3_s)) or 12E-3_henryx(2_a÷(3_s)) or .012_henryx(2_a÷(3_s))

(NOTE: Always put parentheses around a denominator that has 2 or more parts, like 3_s in

2_a/ (3_s)) Otherwise only the first number or variable will be in the denominator.

The above expression results in 8 mV, or .008 volts:

You see that this calculator will not only solve the numbers, it will give you the right units as well. This has another use, not available on any lesser calculator, but needed very much:

If you do not get the right units, this calculator has told you your expression needs correction!

Gone are the days you just write a number down and hope you didn’t get the formula wrong. Now you can know if you got the formula wrong!

4. Solve an equation or expression for any variable, with units

STORE is a way of storing numbers into variables. This allows us to use the variables in formulas and expressions instead of entering numbers the way we must on an ordinary calculator.

For instance, Ohm’s Law is I = V / R.

We can solve for the current if we know the voltage and the resistance. If the voltage is 120 V and the resistance is 33 ohms, we could find the current with the expression

But a better way is to store the values for volts and ohms into their variables, and then just use the standard Ohm’s Law formula. In our calculator, we can store the units right along with the numbers. The above problem can be handled like this:

STORE is the STO key on the lower left side of the keypad.

It gets better. We can do it all on one line by separating lines with the colon “:” key, (2ND 4), like this:

It gets better yet. We can store values and units to every variable, then choose which variable to solve for, like this: Even though i was assigned the value 5 amperes, solve(i=v/r,i) overrode the stored value of i with the calculated value of i.

Note: i still has its stored value (5_a), even though the readout shows its calculated value (3.636_A). You would have to store the calculated value of i into i to change it: 3.636 STOi. I do this by copying the answer into the command line, deleting the i=, and inserting STOi.

We can solve for any variable using this technique.

So you see we can use standard formulas and solve for any variable within them, and get the correct answers with units, without worrying about conversions or algebraic errors.

5. Establish a memory Folder and Variable (=file name) for storing useful equation solvers

This feature really sets this calculator apart: the ability to store formulas, word files, spreadsheets, programs, – – just about anything a computer can do. We can store our command line assignments and solvers into a folder and file (variable) where we may retrieve it at any later time. How much later?

For example, we want to save the electronic formulas we have produced, so we can recall them with ease. The default folder is main, but we may choose a folder with a more significant name, like electron. We are limited to 8 characters beginning with a lowercase letter, with possible numbers and underscores, but no blanks or other punctuation.

Let’s create a folder named courses, and within it, a file named electrnx. Files are called variables in the TI-89, probably as a legacy from much less powerful calculators. Press 2ND VAR-LINK, F1 Manage, 5:Create Folder, ENTER. Now you may key in courses without using the ALPHA key, ENTER, ENTER.

Press HOME to get back to the equation or solver you wanted to save:

Make sure the part to save is highlighted. In the case shown, the Ohm’s Law solver is selected, along with its initial variable stores. That is what we are going to store in a file, or variable, called ect125.

Press yellow diamond, COPY (the key). This copies anything highlighted to the clipboard.

Now we are going to use one of the applications to store this highlighted solver problem. Press the APPS key, and scroll around until you highlight the Text Editor application. Press ENTER.

Select 3:New, ENTER. main will be blinking. Press the right cursor, and scroll down the window and select courses, ENTER. Press the down cursor, and key in ect125, ENTER, ENTER.

[Of course, you may choose whatever folder and variable names you please, within the parameters mentioned above.]

You have created a folder named courses and a file (variable) named ect125. You may see a blank screen.

6. Copy and Paste equation solvers to memory and to the command line

Now you may paste your formula solver into this file. Press PASTE. You should see this:

Any time you need this formula solver with its initial values, you may go to the Text Editor and select Open and select courses and then select ect125 and enter. You will again see the above screen. Much, much more can be saved to this same screen: all your ect125 formulas may be saved here. You will want to name them and space them out so you recognize them and key in any special instructions that go with them.

To select them for use in HOME, you highlight them and press COPY. DO NOT press ENTER at this time, it will destroy anything highlighted, and there is no UNDO!

Then press HOME and PASTE the selected material in the command row.

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