化简求值:(xy^-1-x^-1y)/(x^-1+y^-1),其中x=2,y=-1
问题描述：
化简求值:(xy^-1-x^-1y)/(x^-1+y^-1),其中x=2,y=-1
答
解
(xy^-1-x^-1y)/(x^-1+y^-1)
=(x/y-y/x)/(1/x+1/y)——分子分母同时乘以xy
=(x²-y²)/(y+x)
=(x+y)(x-y)/(y+x)
=x-y
=2-(-1)
=3