Question: absolute value funny thing

Hi there, here are the commands: > y[1]:=exp(1)^(-(1/2)*(u[1]^2+u[2]^2)); > y[2]:=arctan(u[2]/u[1])/(2*Pi); > a:=diff(y[1],u[1]);b:=diff(y[1],u[2]);c:=diff(y[2],u[1]);d:=diff(y[2],u[2]); then it begins > a*d-c*b; g:=abs(simplify(%)); i got the funny "Re" thing in the expression why it didnt give me the answer as I would expected if I use the following command? > a*d-c*b; g:=-1*simplify(%); that's what I wanted the idea is I want the absolute value of the simplified answer ( simpify(%)) what's the difference here?
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