question about the square root of negative 1 ( i )

[alex bennett]

yes the imaginary number, i. My math teacher was telling us something basic about square roots and got off topic with square root of -1, he was saying its imaginary, yet it exists. When power lines are hanged from post to post, they sag, they are not taunt, but at the beginning and end of each wire, they are straight , perfect 90 degrees, because of the thickness, for a little ways, before they begin to sag he said he forgot how/what the square root of -1 is used here, but it is. does anyone (boiling lead bath) ( ) know?