Oh, that is brilliant. Good going.
By the way, you probably shouldn't use
j as a dummy variable if you're going to use
Xjā as a non-dummy variable after that.
I'm confused though, has everything attached properly? 'cause I don't see any mentions of complex numbers anywhere in your picture?
P.S, you can do \cos and \sin to get
cos,sin instead of \mathrm{cos}, \mathrm{sin}