"There is only one thing that concerns me Betty. How can we relate the complex numbers using the 'cis' notation with the old way of naming complex numbers?" "No problem," said Betty. "For a number like 2cis we can see from the diagram that the real part is just 2cos and the imaginary part is 2sin . So 2cis = 2cos + i 2sin = + i In fact we can say that in general rcis = rcos + i rsin = r(cos + i sin) "Yes!" exalted John.