# variable t

Heikki Höijer shared this question 3 years ago

Variable t seems to have a special property: You can draw a line by writing

(1+2t, 3+4t, 5+6t)

on command line.

But if t is already in use, e.g. t = 0, you get only a point, in this case

(1, 3, 5).

So, here is my question: how can you "undefine" a variable? Is the the only solution not to use t as a variable?

(It would be nice to be able to draw a plane with same way, e.g. (1+2t+3s,4+5t+6s,7+8t+9t).)

1

when using parameters, just use letters that aren't yet used elsewhere. It's the same for letters e and i. If they are already used in the names of whatever object, they will stand for the algebraic value of this object, if nor e will automatically be used in calculations as the number of Euler and i as the complex number.

So it has nothing to do with a special property of t, only if it has been used already or not.

If you explicity want to use 't' and it is already used, you can rename the object called t, so t is free as a name to use.

chris

1

TI-nspire has command "delVar", I just thought that maybe Geogebra has something similar.

(But variable t has a special property! As I stated, if you write on the command line "(1+2t, 3+4t, 5+6t)", you get a picture of a line in space. If you use any other variable, you get a slider! A very special property for t, I think...)

1

Indeed, you can use t, x, y or z without problems and others wil ask for a slider.

Instead while using functions you can define f(p)= 2 p +1, f(k)= 2 k +1 or whatever so in using letters as a variable the line case you mentioned seems to behave different from the fuction case

chris