（x根号y-y根号x）除以根号xy,

（x根号y-y根号x）除以根号xy,
（x根号y-y根号x）除以根号xy,

（x根号y-y根号x）除以根号xy,
（x根号y-y根号x）除以根号xy
=(根号x^2y - 根号y^2x)除以根号xy
=根号x-根号y
注：x^2 为x 的平方

原式=(x*y^(1/2))/xy-(y*x^(1/2))/xy
=y^(-1/2)-x^(-1/2)
=根y/y-根x/x