Multiplying by i is a 90-degree counterclockwise rotation. Multiplying by i twice (i.e. by i²) is a 180-degree rotation, which turns 1 into -1. So i² = -1 is not an algebraic trick; it is a rotation.
Table showing polynomials over reals versus complex numbers, demonstrating every degree-n polynomial has exactly n complex roots
| POLYNOM | REELLE NULLSTELLEN | KOMPLEX |
|---|---|---|
| x - 3 = 0 | 1 (x=3) | 1 |
| x² - 4 = 0 | 2 (±2) | 2 |
| x² + 1 = 0 | 0 reelle Nullstellen | 2 (±i) |
| x³ - 1 = 0 | 1 reelle Nullstelle | 3 |
| x⁴ + 4 = 0 | 0 reelle Nullstellen | 4 |
| Jedes Polynom vom Grad n hat genau n komplexe Nullstellen, Vielfachheiten mitgezählt |