The complex number, i, is called an "Imaginary Number". "i" is the answer when you take the square root of negative one. Because you can not take the square root of a negative number, the variable "i" is considered an imaginary number because it doesn't actually exist.
But, lead it to mathmaticians to work with "Imaginary Numbers". Working with "i" leads to a large branch in math because some amazing discoveries have come from it! In later math courses, you will do a great deal of calculations involving the variable "i". Here, we are just giving a basic introduction to "i", the Imaginary Number.
Because the √-1 = 1i = i, it extends to other values under the radical sign.
For example, the first twelve perfect squares are shown below:
√-4 = 2i
√-9 = 3i
√-16 = 4i
√-25 = 5i
√-36 = 6i
√-49 = 7i
√-64 = 8i
√-81 = 9i
√-100 = 10i
√-121 = 11i
√-144 = 12i
Rule: To take the square root of a negative number, take the square root of the positive number under the radical, then add "i" to your answer to show it is an imaginary number.