Question

若xy=m,且1/x的平方+1/y的平方=n,则(x-y)的平方=_______

Answer 1

1/x^2+1/y^2通分=(x^2+y^2)/(xy)^2=n

x^2+y^2=(xy)^2*n=m^2n

(x-y)^2=x^2+y^2-2xy=m^2n-2m