A complex number is a number composed of two parts—a real part and an imaginary part, typically expressed in the form a+bi.  Where a and b are real numbers and i is the square root of -1.  A complex number z can be graphically expressed in the complex plane (see following figure) or may be written in polar form as z = r (cos(ø) + i sin(ø)).  Because cos(ø) + i sin(ø) = EXP(iø), it is also common to express z as r EXP(iø)., where EXP(iø) is the number e to the iø power.