# Unknown

## Unknown

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 $$y$$.