Firstly,将等式x∧2-3xy-4y∧2=0两边同除以y^2(x/y自动意味着y≠0,故曰此步合理) Secondly,由第一步可得：（x/y）^2-3(x/y)-4=0 thirdly,不妨设m=(x/y),则得等式：m^2-3m-4=0,解此一元二次方程得：m=4或者m=-1.At la...