# HP CAS on HP 40gs

The HP CAS system was created by Bernard Parisse of University de Grenoble for the HP 49g calculator. The same CAS Technology was later improved and adapted for inclusion on the HP 40g with the help of Renee De Graeve, Jean-Yves Avenard and Jean Tavenas. The HP CAS system offers the user a vast array of functions and abilities as well as an easy user interface which displays equations as they appear on the page.

To access CAS Equation Writer on the HP 40gs, press [HOME] key and select {CAS} the first soft key on the right.

The HP 40gs (HP40g) also includes the ability to display many algebraic calculations in ‘step-by-step’ mode, making it an invaluable teaching tool in universities and schools. Functions are grouped by category and accessed via menus at the bottom of the screen.

Learning to use the CAS on the HP 40gs is very easy but, as with any powerful tool, to be really effective in its use requires familiarity and time. One way to start is to refer to syntax pages include cross references to related functions and examples which can be pasted into the CAS with the press of a single button. Simply press [Shift] [SYNTAX] from within the CAS Equation Writer screen to access the help.

Example: Factorise the expression (x-4)(x+5)-(x-40)

Here are the steps involved:

• Press [HOME] and press {CAS} soft key to access CAS Equation Writer.

• On the CAS Equation Writer Screen, enter the following key sequence. [(] [X] [-] [4] and the press the [Up Arrow] key 4 times to highlight ‘(X-4)’. Press [*] [(] [X] [+] [5] and press the [Up Arrow] key 4 times to hightlight ‘(X-4)*(X+5)’. Press [-] [(] [X] [-] [4] [0].

• Press [ENTER] to simply the entire expression. Or you can press {ALGB} soft key, and select ‘FACTOR’.

• Now here comes the ‘fun’ part. You can review the history and recall your entry. Press [HOME] and use the Arrow keys to select the step that we want to recall and press [ENTER].

This is particularly useful if it is a multi-step solution.

Click the following link, to see how the same equation is solved using HP 50g.