# Math Help - Functions

1. ## Functions

is it always not a function when you have a negative variable?

2. Originally Posted by Russian
is it always not a function when you have a negative variable?
y = -5x -1 is a function

y = -x is a function

$y = - x^3-2x^2-x+4$ is a function. Please specify clearly your question.

3. Perhaps you are thinking of $\sqrt{x}$ or $log(x)$ which are not defined for negative values of x. But those are properties of those particular functions, not functions in general.

Certainly simple functions, like $x^2$ or 3x- 2 are defined for all values of the variables, negative as well as positive.

4. Originally Posted by HallsofIvy
Perhaps you are thinking of $\sqrt{x}$ or $log(x)$ which are not defined for negative values of x. But those are properties of those particular functions, not functions in general.

Certainly simple functions, like $x^2$ or 3x- 2 are defined for all values of the variables, negative as well as positive.
yes that is what i was thinking.