i is the square root of −1. Imaginary numbers are multiples of i — like 2i, 5i, −7i.
Powers of i cycle
- i¹ = i
- i² = −1
- i³ = −i
- i⁴ = 1, then it repeats
They're called 'imaginary' for historical reasons — but they describe real things, like AC circuits and quantum waves.