Hey, So the other day I was at this bookstore looking for a cheap book on differential equations to buy... when I found one in the Arabic section. (Over here English books on math are atleast $60USD even if they're around 200-400pages.. kind of a rip off..) So I saw some books in an "Advanced Mathematics for Engineers" series... But what kind of perplexed me was how book 1 pretty much focused on functions of a complex variable and book 2 then introduced differential equations. This brings up two things to mind.. 1) Of what use is functions of a complex variable to engineers? What exactly can it be applied to, and what can only be described with complex functions? 2) Would it be absolutely required to have a course in complex variables first before learning about differential equations? Thanks a lot for any input.