## Function or not?

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### Function or not?

I'v got problems like this:
Code: Select all
`{(x,y) : y^2 = x }`

and I have to state wether it is a function or not.

Code: Select all
`so, let y = 2(2)^2 = 4`

Code: Select all
`let y = -2(-2) ^2 = 4`

= not a function because (4,2), (4,-2).

but i encountered this problem:

Code: Select all
`{(x,y) :|x + y| = 4 }`

and I have no idea how to know if it is a function or not and demonstrate it like i did with the other one. Thanks.
Cohiba

Posts: 125
Joined: Mon Jul 04, 2005 12:42 pm

Let y = 0.
What value(s) can x have? If there is more than one value that x can have then y(x) is not a function.
Need information on a function I've posted? Chances are it's at the MSDN.
MXP

Posts: 6506
Joined: Mon Sep 22, 2003 5:27 pm

You are wrong Colin. By definition, a function is an equation where there aren't 2 y-values for the same x.

t i l e x

Posts: 3604
Joined: Wed Dec 03, 2003 3:59 pm

Err, I was backwards. Let me rephrase:

Let x = 0.
What value(s) can y have? If there is more than one value that y can have then y(x) is not a function.

Need information on a function I've posted? Chances are it's at the MSDN.
MXP

Posts: 6506
Joined: Mon Sep 22, 2003 5:27 pm

let x = 0
|y + x| = 4
|y| = 4
y = 4 or y = -4

(0,4), (0,-4). so, not a function.

Thanks guys.
Cohiba

Posts: 125
Joined: Mon Jul 04, 2005 12:42 pm