A number that is the square of a whole number.

### Examples

16 is a perfect square because 4² = 16 and 4 is a whole number.

20 is not a perfect square because \(\sqrt {20}\) is not a whole number.

### Educational Note

The expression “perfect square” should not be applied to any algebraic expression.

So, the trinomial *x*² – 4*x* + 4 which is equal to (*x* – 2)² can only be called a perfect square if *x* – 2 is a whole number. Instead, we should say that the trinomial *x*² – 4*x* + 4 is the square of the binomial (*x* – 2).