The app below illustrates multiplication of complex numbers in the complex plane. The point C is a complex number represented as a vector generated from a real component, a, and an imaginary component, b. So C=a+bi. D is another complex number represented as a vector in the complex plane. E represents the product CD. Move point C by changing (sliding) the values of a and b. Move D around in the plane. Note how the product, E, changes.