I know what a complex number is. Learned it way back when I took college classes. I know it is a number that has a real and imaginary part of the form a + bi. What I have always failed to understand is what conceptually does it mean. I know what i is , it's the square root of -1. I just could never understand what it means to say that a number has a real and imaginary part. And that the imaginary part lies perpendicular to the real part. So an imaginary number seems like a two-dimensional vector . Beyond this however I fail to understand how imaginary number came to be and what its underlying meaning is. Note, I accidentally put imaginary number on this post I tried to go back and rename the post but I could not figure out how to do it in Tapatalk.