Question

[LGB]

I have a few questions i'm hoping someone could answer. These are probably no-brainers, but I am frustrated. I am trying to figure out how to restrict the domain of a function when i type it into the calculator.

I am trying to something like this:

4x+24 when x<2 and x>-2.

Any help would be appreciated.

Thanks.

[Harrierfalcon]

If there's only one domain restriction, just press [Window] and change XMin to the lower restriction and XMax to the upper restriction.

[LGB]

I am going to have to restrict more than one thing, as I am writing my name using the graphs of functions. The example I just one part of my problem, but once I know how to restrict one, I should be able to do them all. Is there any other way it can be done?

[Noob88]

Try (4x+24)/((x<2) and (x>-2))

[LGB]

I tried doing what you said, but even when I change the X and Y min and max, when I graph my line, it changes the Min and Max to fit the line, not the other way around. I'm not sure why or what to do.

[LGB]

[Noob88]

Division bar... You take an equation and divide by the restrictions... I believe that will work out for what you want, forgive me if I misunderstood

[LGB]

Gah, well thanks, but it isn't working. I punch that in and press graph, and the calculator says it's busy as if it's graphing something, but nothing shows up on the screen. I put in the vertical bar instead of the division bar, and that restricted it somewhat, as the line goes to -2 and stops, but not on the positive side.

Talk about frustrating.

[JoostinOnline]

You should be able to eliminate the and from the equation, unless it is necessary on the 89. I don't know why your equation wouldn't work to begin with though. If you accidentally typed (4x+24)/((x<-2) and (x>2)) then that would explain getting nothing on your graph though.

[DarkerLine]

when(-2<x and x<2,4x+24,undef)

This should work.

[Liazon]

[DarkerLine]

The vertical bar can't do anything other than substitute values unless you have a solve()-type expression.

The problem with (4x+24)/(-2<x and x<2) is that on the TI-89, logic values have their own data type instead of using 0 and 1 as on the TI-83+. So the expression is evaluated either to (4x+24)/true or (4x+24)/false, both of which are sufficiently stupid that they don't get graphed.

The when() command is pretty much always the right choice for any piecewise definition. Sure, sometimes another command will work, but it will never be as simple to understand.

[Liazon]

thanks for clearing that up.