若[1/2(x+y)]的二次方-[1/2(x-y)]的二次方

问题描述:

若[1/2(x+y)]的二次方-[1/2(x-y)]的二次方

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