# Math Help - Define Function

1. ## Define Function

Tell me, why is x = |y| NOT a function?

Also, would y = |x| be a function? If so, why?

2. Originally Posted by sharkman
Tell me, why is x = |y| NOT a function?

Also, would y = |x| be a function? If so, why?
A function is where a value of x corresponds to exactly one value of y.

With this equation it is clear that f(-4) = f(4) and so is not a function

3. ## So...

Originally Posted by e^(i*pi)
A function is where a value of x corresponds to exactly one value of y.

With this equation it is clear that f(-4) = f(4) and so is not a function
So, x = |y| means that y varies in terms of values and thus making this equation NOT a function, right?

Is that what makes it different from y = |x|?

4. Because you can plug in any value of x and you can be guaranteed to get exactly one value of y out the other end. That's what defines a function: every value of x has exactly one value of y.

5. ## ok...

Originally Posted by Matt Westwood
Because you can plug in any value of x and you can be guaranteed to get exactly one value of y out the other end. That's what defines a function: every value of x has exactly one value of y.
Easily explained.