( f(x,y)=xe-2x²-2y² ):
a) ( f(x,y) = xe-2x²-2y² )
b) ( f(x,y) = x²e-2x²-2y² )
c) ( f(x,y) = e-2x²-2y² )
d) ( f(x,y) = x²e2x²+2y² )