The polar form of a complex number is equal to a real number expressed as a angle’s cosine, and the imaginary number (i) times the same angle’s sine, with the angle expressed in radians (for more about angles, sines, cosines, and polar forms, see “Geometry and Trigonometry”). This is seen in equation form as: r(cos θ + i sin θ), in which r is the radius vector, θ is the angle, and i is the imaginary number.