In this algebra video the instructor shows how to work with complex numbers. When you have a positive number under the square root, you can easily find its value by writing it in the form of product of numbers, and then solving. That is, to find the square root of a positive number, you can find another number which multiplied by itself gives the original number. This new number becomes the square root of the original number. But when you are asked to find out the square root of a negative number, you cannot find such a number which multiplied by itself gives a negative number because a positive number multiplied by itself is positive and a negative number multiplied by itself is again positive and not negative. Therefore, the square root of a negative number cannot be any identifiable real number, and it is a complex number. This video teaches about complex numbers.