finding domains of functions

[steve]

I'm hoping someone will help me out with finding domains on the TI-89.


example: f(x)= 1/x^2-x. Now I realize that x cannot = 0,1. My problem is trying to check my work on the 89. I'm not sure if I should use the Y editor, or solve. I downloaded a few flash apps from TI, but found no file for finding domain or range at all.

If someone could please give me some direction I would greatly appreciate it. Perhaps someone knows of a file or application I could download onto my 89 that would help me out?

Thank you very much.

[mellamokb]

Hi steve,

I don't know of any programs / apps that can determine domains and / or ranges because that is a very complex problem. However, there is a simple way to find some holes in a function. Whenever the reciprocal of a function evaluates to 0, there is a hole at that location (because the reciprocal of 0 does not exist):

"solve((f(x))^(-1)=0,x)" will output "x=0 or x=1"

So try to solve the reciprocal equal to zero using "^(-1)" applied to the function and you should get the x-coordinates of most types of holes in the function.

Hope this helps!

~ mellamokb

[steve]

Thanks... I discovered roughly what you described late last night with using solve. You're right they are very complex, and thanks for your help.