Complex number
A number of the form a + bi, where i is the imaginary unit with i² = −1.
A complex number has a real part a and an imaginary part b. Complex numbers extend the reals so that every polynomial equation has a root and so that operations like square roots of negative numbers make sense. The modulus |a + bi| = √(a² + b²) is its distance from the origin in the complex plane.
Formula
z = a + bi, |z| = √(a² + b²)