The significance of the sq root of minus 1 is that historically it is a controversial calculation. The result of the calculation, 1i, brought about a whole new set of numbers, "imaginary numbers". If you think of "normal" numbers as a line going horisontally, say -3 -2 -1 0 1 2 3, the imaginary numbers' line goes vertically crossing the the "normal" numbers' line at point 0.

Karl Marx wrote a paper slamming the possibility of imaginary numbers...