Cube Root I Bd32F3
1. **State the problem:** Find the cube roots of the complex number $i$.
2. **Formula and explanation:** To find the cube roots of a complex number, express it in polar form $z = r(\cos \theta + i \sin \theta)$, then use De Moivre's theorem:
$$\sqrt[3]{z} = r^{1/3} \left( \cos \frac{\theta + 2k\pi}{3} + i \sin \frac{\theta + 2k\pi}{3} \right)$$
where $k = 0, 1, 2$ for the three cube roots.
3. **Convert $i$ to polar form:**
- The complex number $i$ is $0 + 1i$.
- Its magnitude is $r = |i| = 1$.
- Its argument (angle) is $\theta = \frac{\pi}{2}$ because it lies on the positive imaginary axis.
4. **Calculate cube roots:**
- Magnitude of cube roots: $r^{1/3} = 1^{1/3} = 1$.
- Angles for cube roots:
- For $k=0$: $\frac{\pi/2 + 2\cdot0\cdot\pi}{3} = \frac{\pi}{6}$
- For $k=1$: $\frac{\pi/2 + 2\cdot1\cdot\pi}{3} = \frac{\pi/2 + 2\pi}{3} = \frac{5\pi}{6}$
- For $k=2$: $\frac{\pi/2 + 2\cdot2\cdot\pi}{3} = \frac{\pi/2 + 4\pi}{3} = \frac{9\pi}{6} = \frac{3\pi}{2}$
5. **Write cube roots in rectangular form:**
- For $k=0$:
$$\cos \frac{\pi}{6} + i \sin \frac{\pi}{6} = \frac{\sqrt{3}}{2} + \frac{1}{2}i$$
- For $k=1$:
$$\cos \frac{5\pi}{6} + i \sin \frac{5\pi}{6} = -\frac{\sqrt{3}}{2} + \frac{1}{2}i$$
- For $k=2$:
$$\cos \frac{3\pi}{2} + i \sin \frac{3\pi}{2} = 0 - 1i = -i$$
6. **Final answer:** The three cube roots of $i$ are
$$\frac{\sqrt{3}}{2} + \frac{1}{2}i, \quad -\frac{\sqrt{3}}{2} + \frac{1}{2}i, \quad -i.$$