code: public static ComplexNumber Subtract(ComplexNumber z1, ComplexNumber z2) {
          return new ComplexNumber(z1.real - z2.real, z1.imaginary - z2.imaginary);
      }
docs: Subtract two complex numbers.
  
  @param z1 Complex Number.
  @param z2 Complex Number.
  @return Returns new ComplexNumber instance containing the subtract of specified complex numbers.