Input value - |-0|1|2|1|0|
Output Value-|-4|-2|0|2|4|

how can I tell when anything is a function?

Im confused of this.
Help pleeaseee:o

A function assigns each element x of A exactly one element y of E.

Suppose we have a circle with radius 1. It has equation

If we plug in x=1/2, we get two different outputs.





See? Two different results for the same input. NOT a function.

Say we have . A parabola with vertex at (0,0).

If we have

This IS a function. See the difference?

Also, if we can pass a vertical line through its graph only once, then it is a function. A circle we can pass a vertical line through twice. Not a function.

The parabola x^2 we can only pass a vertical line through once. A function.



Google them and you'll find lots. Here's one: http://www.themathpage.com/aprecalc/functions.htm