The imaginary unit i is defined such that i²=-1. So what's i³? i³=i²⋅i=-i. What's i⁴? i⁴=i²⋅i²=(-1)²=1. What's i⁵? i⁵=i⁴⋅i=1⋅i=i. This pattern repeats itself all the time, so we can quickly tell what iⁿ for any positive integer n.
License: CC BY-NC-SA by Khan Academy