Complex numbers \(z = x + iy = r e^{i\theta}\) in the Argand plane \(\mathbb{C}\). Holomorphic functions \(f(z) = u(x,y) + i v(x,y)\) satisfy the Cauchy-Riemann equations \(\frac{\partial u}{\partial x} = \frac{\partial v}{\partial y}\) and \(\frac{\partial u}{\partial y} = -\frac{\partial v}{\partial x}\). Conformal maps preserve angles and local geometry. Roots of unity \(z^n = 1 \implies z_k = e^{i 2\pi k / n}\) form regular vertices of cyclic polygons in the unit circle.