Ineed a detailed explanation of how x^2-4x+4 factored= (x-2)(x-2) wouldnt the two negative signs cancel each other out?

Well, yes and no.  If you are multiplying two terms like (x - 2) and (x - 2), you would use the FOIL method -- first, inside, outside, last.  See the attached diagram.  The two negative signs would cancel each other out only when multiplying the last values.  Let me know if you need further explanation.