question about functions (no calculations)

[unreal pilot]

how do you know when an equation is a function

[unreal pilot]

The question is asking to give the reciproqual function and to say whether its a function or not

I already found them but idk how to tell if its a function or not

[drifting fern]

A function returns only one number

When you write $y = x^2-4$,
You have probably found
$x^2 = y+4$
When you choose y ( larger than -4) there are two values for $x$ that work

[heady spade]

Daddy_314

[drifting fern]

$x = \sqrt{y+4}$ or $x = -\sqrt{y+4}$

[heady spade]

Daddy_314

[drifting fern]

Since we have two options for x, this cannot be a function

[fallen sun]

vertical line test

easy peasy

[unreal pilot]

Ahh ok