x²-y²=20,{(x-y)²+4xy}{(x+y)²-4xy}的值
问题描述:
x²-y²=20,{(x-y)²+4xy}{(x+y)²-4xy}的值
答
,{(x-y)²+4xy}{(x+y)²-4xy}
=(x²-2xy+y²)(x²+2xy+y²-4xy)
=(x²+2xy+y²)(x²-2xy+y²)
=(x+y)²(x-y)²
=[(x+y)(x-y)]²
=(x²-y²)²
=20²
=400