2x-y=2 xy=2///////4x²-6xy+y²=?
问题描述：
2x-y=2 xy=2///////4x²-6xy+y²=?
答
4x²-6xy+y²
=（4x²-4xy+y²)-2xy
=(2x-y)²-2xy
=2²-2×2
=0