Topic: The Imaginary Unit

Square Roots of Negative Numbers

In precalculus, understanding how to work with square roots of negative numbers is essential for exploring complex numbers. While the square roots of positive numbers are real, the square roots of negative numbers are not real and require the use of the imaginary unit.

• Square Roots of Positive Numbers: These are real numbers. For example:

• Square Roots of Negative Numbers: These are not real numbers. For example:

The Imaginary Unit

To express the square root of negative numbers, mathematicians use the imaginary unit, denoted by i:

• Definition:

• Any square root of a negative number can be written in terms of i. For example: , where is a positive, real number.

Factoring to Separate the Negative in the Square Root

When simplifying square roots of negative numbers, factor out the negative sign and use the imaginary unit:

• Example: Simplify

• General Rule:

Practice Examples

• Example 1: Simplify

• Example 2: Simplify

Summary Table: Real vs. Imaginary Square Roots

Note: Solutions that include the imaginary unit are called imaginary numbers.