At last reply:

http://www.mathhelpforum.com/math-he...-new-post.html

Deveno given an example like what $\displaystyle (a+ai)(a-ai)=0$

Here another complex number discussion recently:

http://www.mathhelpforum.com/math-he...rm-184791.html

If rewrite two complex numbers to polar form and multiple with other one. I get a difference result: $\displaystyle 2a^2$ (i.e. real part only)

What I'm missing?