先化简 再求值【（x平方+y平方）的平方-4x平方y平方】/（x+y）平方
问题描述：
先化简 再求值【（x平方+y平方）的平方-4x平方y平方】/（x+y）平方
答
【（x²+y²）²-4x²y²】/（x+y）²
=(x²+y²+2xy)(x²+y²-2xy)/(x²+y²+2xy)
=x²+y²-2xy
答
=[(x4+2x2y2+y4)-4x2y2]/(x+y)2
=[x4-2x2y2+y4]/(x+y)2
=[(x2-y2)2]/(x+y)2
=[(x-y)(x+y)]2/(x+y)2
=(x-y)2
答
原式=(x²+y²+2xy)(x²+y²-2xy)/(x+y)²
=(x+y)²(x-y)²/(x+y)²
=(x-y)²