x^2*y^2+9x^2+y^2-12xy=9(x^2*y^2-6xy)+(9x^2+y^2-6xy)=9(x^2*y^2-6xy+9)+(9x^2+y^2-6xy)=9+9(xy-3)^2+(3x-y)^2=18因为x,y是非负整数,所以(xy-3)^2的值(3x-y)^2的值只能在0,1,4,9,16中选那么只有9+9=18所以(xy-3)^2=...