When we raise a positive number or a negative number to an even exponent, the result is always a positive number.

**Example:**

**(-4)² = (-4)(-4) = 16**

and**(+4)² = (+4)(+4) = 16**

However, as in mathematics the result of an operation must be unique, it is defined that:

Generically:

Any even index root of a positive number is the**positive number**that raised to the exponent corresponding to that index equals the given number.

*Note*:

There is no real root of a negative number if the index is even.

**Example**:

doesn't exist because there is no real number that squared gives **- 4**.