Complex Numbers

A complex number is a number of the form a + bi, where a and b are real numbers and i is the imaginary unit, the square root of –1.

In a complex number z = a + bi, a is called the "real part" of z and b is called the "imaginary part". If b = 0, the complex number is a real number; if a = 0, then the complex number is "purely imaginary."