Thread: how can I tell whether an equation is a function or not

hello everybody

I would like to know how can I know whether an equation is a function or not

for example x^2+y^2= 9 , I know this is not a function because it doesn't pass the vertical line test, but is any way to tell algebraically if its a function or not?
thank you.

Originally Posted by jhonwashington

hello everybody

I would like to know how can I know whether an equation is a function or not

for example x^2+y^2= 9 , I know this is not a function because it doesn't pass the vertical line test, but is any way to tell algebraically if its a function or not?
thank you.

It means,
"Can for the same value of x be two distint values of y (at least)"
The answer is yes.

Consider,
x=1
We have,
y=sqrt(8) and y=-sqrt(8)