# What are imaginary numbers?

Imaginary numbers are any numbers that include the imaginary number i. A mix of imaginary and real numbers gives you what’s called a complex number.

The primary reason we use imaginary numbers is to give us a way to find the root (radical) of a negative number. There’s no way to use real numbers to find the root of a negative number, which prevents us from solving even simple polynomial equations.

But with imaginary numbers, we define the square root of -1 as the imaginary number i, and that allows us to easily find the roots of imaginary numbers.

0:21 Are imaginary numbers real numbers?

0:45 Examples of real and imaginary numbers

1:22 The definition of the imaginary number i

1:39 Why do we need imaginary numbers?

1:53 Why is the imaginary number helpful?

2:52 What happens when you square the imaginary number?