couple of questions

[rrossorr]

hi,

I've been getting into programming my TI-89 to help ease my engineering calculations.

I have a couple questions:

(1). How do you make a function that has an optional parameter? For example, when you use to differentiate function, your parameters are: expression,variable[,order]

and you can either enter d(x^2,x) and it will give you the first derivative, or you can enter d(x^2,x,2) and it will give you the 2nd derivative.

(2). How can I make a custom hotkey? As an engineer there is a certain mathmatical calculations I have to make a LOT, and it would be so much easier if there was just a single key to achieve it (kind of like my own custom operation sign). Is this possible?

[mellamokb]

Hi rrossorr,

(1) I don't believe that functions can take optional parameters. You can simulate optional parameters by using a certain value that your function will ignore, like -1. For instance, here is a function that returns the area of a square or rectangle; the second parameter is "optional" (signified by -1). If only one parameter is provided, that is assumed to be the side length of a square; the second parameter is the width of a rectangle: