what number should be added to complete the square using: x^2-4x

Given an equation of the form x^2+Ax=0, you complete the square by dividing value of the coefficient of x by 2 and squaring it, which gives you (A/2)^2. Here’s an example: given x^2 - 10x, you have A= -10, so you complete the square by adding (-10/2)^2 = (-5)^2 = 25. You end up with x^2-10x+25, which factors to (x-5)^2. Now apply this method to your problem, and feel free to post your answer back here.