Name given to a missing value.

The term “unknown” is used for a missing value in a relationship.

In an equation like \(y = x + 3\), the letters \(y\) and \(x\) are called variables.

### Examples

- In the equation \(2y + 7 = 21\), the unknown is \(y\).
- In the equation 5\({y}^{2}\)= 125, the unknown is \(y\).