Excellent Tool for the Classroom or Office

I upgraded from my TI-83 to my 89 as a Sophomore in High School. I now keep it with me at work, and have used it in many different academic and professional situations. IT is an incredibly powerful tool, and I'll try to tell you why I'm so happy with it.

Layout
Moving from the 83 to the 89 was a bit hard at first. The 89 offers a sort of desktop with a menu bar across the top of the screen. The dropdown menus can be used to access common tasks such as clearing the screen, solving or expanding an equation, integrating or differentiating a function, or even writing and storing your own functions. There is an input bar that let's you write equations at the bottom of the screen, while you can see previous work right above you. The top menu bar can be switched with a customizable menu bar that you can tweak to your liking. Switching between the two is just a 2 buttons away.

The keyboard layout has a lot of shortcuts on it. There are 3 buttons (2 normal and 1 alphabetical) that allow selection of alternate commands from a button; that is, each button has a main graphic on it to tell you what it usually does, but it has some color coded graphics around it telling you what it can do if you choose a different function button first. Each button has the main function plus two extra functions. There are even some hidden options that aren't labeled (not enough room?). For example, if you hit the green diamond and "x", you get "&". The standard numeric keys and math operations are all together near the bottom for easy use, making it pretty easy to use. You can move pretty fast on this thing if you don't mind giving your thumbs a good workout.

Functionality
This is by far the most powerful calculator I've ever used. It has the all the arithematic buttons, as well as a full array of algebraic, matrix algebraic, trig, and calculus functions.

The algebra and matrix algebra stuff is really convenient. The equation solver is fantastic. Type in "solve(x+y=3 and x-y=4,x)" and it will tell you what both x and y equal. This may not seem like a huge deal, but when you get to the end of a thermal design problem and have a system of 4 equations with 4 unknowns, you'll save yourself 10 minute on a 55 minute test with this feature. You can also expand and factor equations, find zeros in a function, find common denominators, and much more. You can also enter and save matrices and operate on them, including inverting and multiplying or finding the determinate. Finally, you can enter lists and do analysis on them such as finding the linearity or standard deviation, finding curve fits, or comparing it to another list.

Trig functions include the typical sine, cosine, and tangent. It also offers the inverse trig functions, the hyperbolic trig functions, and the inverse hyperbolic trig functions. These are fully integrated into the solvers, too. If you ask it to solve "sin(x)=0", it will give you this answer: "180@n1". That may seem strange, but the syntax represents an answer and the subsequent answers since the function is cyclic. I know this might not be clear, but it's all spelled out in the exhaustive solution manual.

The calculus features are what really make this stand out to me. On the 83, you could only do numeric integration and derivation. This means that you can take the derivative of f(x)=x^2 with respect to x when x=3, because the result is a number, but you couldn't just take the derivative of f(x)=x^2 with respect to x because the result is a function (f'(x)=2x). Now, though, you can! Can't remember the integration rule for cotangent? Just type it in. It will still do numeric, but only if you want it to. You can also do limits including indefinite. This means if you ask it what the limit of 1/x is as x approaches 0, it will tell you it's undefined. Even better, if you tell it to take the limit from the left, it will tell you it's negative infinity! You can also take integrals to infinity, though it doesn't always give you the right answer. It gets kinda confused. If you take the integral of x from zero to infinity, it gives you 8.295E27, which is... infinity-esque.

This is a graphing calculator, right? Somehow, this feature seems minor compared to all the rest. You can graph in multiple modes (x and y, parametric, polar, 3d, and more). You can find the minimum or max on a graph, or find the intersection between two lines. There are many options to automatically or manually adjust your view window, and you can even find features like points of inflection or derivatives at a point. The 3d graphing also provides a rotation feature, which is cooler than it is practical. You can even hold down the arrow and it will rotate even after you let go, stopping only when you tell it to. Fun, but not very useful. :)

Use
The layout makes general use very easy. One great upgrade is the ability to type in your own functions. On the 83, you'd have to find the function names (sine, for example) and select it. Now, you can just type in "sin(" and it will know you want to take the sine. This isn't as key for basic trig since there are buttons, but the first time you have to go digging for "and" or the determinate command, you'll appreciate just typing it in.

A bane of my use with the 83 was trying to keep track of parentheses. After all, did I want (((2a)^(b+2))/(c-(3-x^2)^2))^(2/3) or (((2a)^b+2)/(c-(3-x^2)^2))^2)/3)? That's even hard to type here! On the 89, you can turn on "Pretty Print" which will take your jumbled up mess and actually spread it out and make it into what you'd right on paper. Numerators are drawn over denominators, exponents are superscripts, etc! Just type it in, hit enter, and make sure that's what you meant. This saves me a lot of headaches.

During normal use, many users will need to use an old answer with a current question. If you want to take 1/((4-a)^2+a) and you just calculated [a], you can just choose the answer from previous lines of history. Type all your other stuff, and just scroll up when you need that [a]. This saves me a lot of time. On the 83, it was harder to get the Ans in the right spot in the equation sometimes.

Something I've found useful is the program and text-storing capabilities. Many of my college classes allow notes on exams (Mechanical Engineering), so I sometimes opt to put stuff in the calc instead of on paper. Not only is it always in front of me, but I can write a program to make stuff faster. The programming is really easy, and it can save me from doing the same repetitive steps over and over. This is particularly useful on college exams where time is not on your side. And by that, I mean it's particularly useful on ALL college exams.

Other noteworthy features include the auto-off function that will save you some AA batteries (it takes 4 and a lithium for backup) and the ability to change the screen brightness as necessary. You can also hook your calculator up to another to transfer programs and files, or (with another purchase) hook it up to your computer to work on there or to grab apps from the internet. Also, there is a catalog feature that holds all of the standard and user-defined functions. It also tells you what arguments it needs in case you can't figure out why it won't go. For example, it tells you that the solve command needs two arguments: "equation" (what you're trying to solve) and "var" (the variable whose value you want)

Conclusion
I am very happy with this calculator, and when mine was stolen my freshmen year, I went right out and replaced it. Though expensive, the savings to my time both in and out of the classroom have been awesome, and the extra power saves me from making some stupid algebra mistakes. It's really packed with functions and extras (it even comes with a list of unit conversions). If you're in any math that's algebra level or beyond, you could get a lot of use out of this. Be sure to check with teachers/professors about their classroom calculator rules, since some do not allow them. I've been able to use it in all my college classes except the pure math classes (Calc I, II, III, DifEQ I and II). Also, the ACT does not allow this calculator, so don't throw away that old 83!