1）如果x和y都大于0,则x^2+y根号xy=420=根号x*(x根号x+y根号y)y^2+x根号xy=280=根号y*(x根号x+y根号y)两式相除,有420/280=根号(x/y)3/2=根号(x/y)x/y=9/4x=9y/4带入y^2+x根号xy=280,有y^2+9y/4*根号(9/4*y^2)=280y^2...