# How do you decide whether the relation #7x^2+y^2=1# defines a function?

##### 1 Answer

Jun 14, 2018

It doesn't because one input value yields more than one output value.

#### Explanation:

A function is simply a rule that states how the inputs and outputs must be related.

For example,

In your case, if we solve the expression for

That

Since it is not true that every input yields **one and only one** output, this is not a function.