code: public static ComplexNumber Multiply(ComplexNumber z1, ComplexNumber z2) {
          double z1R = z1.real, z1I = z1.imaginary;
          double z2R = z2.real, z2I = z2.imaginary;
  
          return new ComplexNumber(z1R * z2R - z1I * z2I, z1R * z2I + z1I * z2R);
      }
docs: Multiply two complex numbers.
  
  @param z1 Complex Number.
  @param z2 Complex Number.
  @return Returns new ComplexNumber instance containing the multiply of specified complex numbers.