Imaginary number
Multiplying two imaginary numbers is a lot like multiplying a positive number with a negative number. If we say "go east by 2 × -3 miles", it means "rotate all of the way around (so that you are now facing west) and go 2×3 = 6 miles". Imaginary numbers work the same, except that you can rotate part way. If we say go "east by 2×3i miles", it means the same as if we had said "rotate until you are facing north, and then go 2×3 = 6 miles"