xy分之x的平方-y的平方除以(x-y)
问题描述：
xy分之x的平方-y的平方除以(x-y)
答
=(x+y)(x-y)/xy ×1/(x-y)
=(x+y)/xy
xy分之x的平方-y的平方除以(x-y)
=(x+y)(x-y)/xy ×1/(x-y)
=(x+y)/xy