Welcome to chapter 3, now we will learn about equations and variables and how to use them. Equations are important because thay solve math problems. That is why we use calulators. (If you bought a TI83 to play games, you should have gotten a gameboy.)

An equation is as follows: `2+2=4`.
This is a pretty simple. Then we have more complex equations: `2+(3*4)/2, 4+a=5, sin(25)*n=45.4,`
etc... We will start with simple ones. At the user screen, type `2+2`. You should get 4.
DUH. Now we will type in `4*3+6`, and then type in`4*(3+6)`.
You should get different answers. This is due to the order of operations. For those who don't know,
or don't remeber, here they are:

- Operations in Parethesizes "( )"
- MATH menu operations, like abs(), sqrt(), etc... (NOT >frac)
- Multiplication and division from left to right
- Addition and subtraction from left to right

Example of inputing an equation |

You can recall an answer from
the last equation you put in. Press: **[2ND] [(-)]** (ANS).
This will put `ANS` on your screen. This variable stores the answer to the last
equation you put in. If you want to recall a whole equation, press **[2ND] [ENTER] (ENTRY)**.
And the whole last equation you entered in will be on screen. If you press **(ENTRY)*** you
will see the second to last equation you put in.

** = (From now on, any fuction that requires the [2ND]
key (in yellow on the keyboard) will be in parethesizes and in bold)*

Variable are place holder for numbers.
They are inmportant in that they store answers to equations and they can be used in place
of numbers in equations. Here is how you store a number in a variable:
`2+2->A` (Press **[STO>]** for ->) You can use any letter
to store an answer or number. That means you can store up to 26 numbers in variables.
(You cannot use words as variables, like HI, the calculator interprets this as multiplication (H*I).)
To recall the contents of a variable type its letter.
`A` will produce 4 on screen.
You can also use them in other equations, like: `A-2` and press
**[ENTER]** you will get 2.

Storing an answer in a variable |

Recalling the contents of a variable |

Using a variable in an equation |

As I told you before, variables hold numbers. However, this is a over simplified view.
On the TI 83, variables may hold complex numbers, lists, strings (text like "Hello")
, etc. **Don't worry about this, as they will not come up often,
until chapter 9 (Advanced topics). I will expand greatly on these then.**

So what did you think? Please E-mail me your suggestions (good or bad) to jwtatay@wi.rr.com.

With this lesson mastered, you may move on to Chapter 4.

Or you may go back to the table of contents.