# function notation

• 10 Feb 2018, 7:46 AM
mathsbrain
function notation
Hi,

A bit confused with the use of the notation y=f(x). If we have the circle x^2+y^2=1, we can obviously rearrange and make y the subject which gives y=+-(1-x^2)^0.5. Is it wrong to write f(x)=+-(1-x^2)^0.5 since this is not a function hence we can't use f(x)?
If so, does that also mean whenever we are given f(x)=..., we can assume the given relation must be a function?
• 10 Feb 2018, 9:27 AM
fan96
Re: function notation
$x^2 + y^2 = 1$ is not a function. It is not correct to write it as one.

The function notation $f(x)$ should only be used with functions.
• 10 Feb 2018, 10:44 AM
HeroWise
Re: function notation
THere is an imaginary vertical line test to prove if a graph is a function or not