4 R f . ( R , R , ) (a) R={(x,y)R2x2+y28},f(x,y)=x2+y2+2x2y (b) R=1,11,1]R2,f(x,y)=xy (c) R={(x,y,z)R3x2+y2+z21},f(x,y,z)=xy+z 4 R f . ( R , R , ) (a) R={(x,y)R2x2+y28},f(x,y)=x2+y2+2x2y (b) R=1,11,1]R2,f(x,y)=xy (c) R={(x,y,z)R3x2+y2+z21},f(x,y,z)=xy+z