x-2y=3,
两边平方,
x²-4xy+4y²=9 (1)
x²-2xy+4y²=11(2)
两式相减,
2xy=2
xy=1
x²y-2xy²这题是不是少了y
=xy(x-2y)
=1×3
=3
因式分解:
-x²+4x-4
=-(x²-4x+4)
=-(x-2)²
4x³-4x²y-（x-y）
=4x²(x-y)-(x-y)
=(x-y)(4x²-1)
=(x-y)(2x+1)(2x-1)