Determine whether a function

[lilpotpie]

I'm supposed to determine whether a list of relations are functions, but I'm totally brain dead right now and cannot remember how to do so even reading my book... a couple of the problems are:

x^2 = 1 + y^2


and


y = sqrtx-1

can someone point me in the right direction? Thanks.

 

[morson]

Basically, if you can draw a vertical line through the relation and it intersects it once and only once, it is a function.

 

[jwpaine]

A function has one output for every input.

y = x^2 is a function, because you can plug in any value for x and always come out with a single answer for y.

Graphically, you can check with the vertical line test. Does a vertical line intersect the graph of the function in more than one place? If it does, than it isn't a function.

One of the equations you gave, is not a function.



Hope this helps!