计算:xy(x^-1+y^-1)

问题描述:

计算:xy(x^-1+y^-1)
x^-1-y^-1/ [(x^-2)-(y^-2)]

xy(x^-1+y^-1)=x+y
x^-1-y^-1/ [(x^-2)-(y^-2)]
=1/(1/x+1/y)
=xy/(x+y)