# Is the equation #x^2+y^2=4# a function?

##### 1 Answer

Mar 25, 2017

#### Answer:

No - there is more than one

#### Explanation:

Equations in the form of

graph{x^2+y^2-4=0 [-7.023, 7.024, -3.51, 3.513]}

Is this a function? That is, does there exist a single

This is often called the "vertical line test" - if you draw a vertical line for any value of