Question

计算：(x+y)²-4(x+y)(x-y)+4(x-y)²

2.已知x=y=5,xy=-6,求3x²+3y²

Answer 1

解(x+y)²-4(x+y)(x-y)+4(x-y)²
=(x+y)²-2(x+y)×2(x-y)+[2(x-y)]²
=[x+y-2（x-y）]^2
=(3y-x）^2

Answer 2

(x+y)²-4(x+y)(x-y)+4(x-y)²
=[(x+y)-2(x-y)]²
=(x+y-2x+2y)²
=(-x+3y)²
=x²-6xy+9y²

已知x+y=5,xy=-6,求3x²+3y²
3x²+3y²
=3(x²+y²)
=3[(x+y)²-2xy]
=3×(25+12)
=111

Answer 3

追问

你下面那题错了

追答

错了。。。。我无语，，，

Answer 4

(x+y)²-4(x+y)(x-y)+4(x-y)²
=【(x+y)-2(x-y)】²
=(3y-x)²

Answer 5

原式=[(x+y)-2(x-y)]²

=(x+y-2x+2y)²

=(3y-x)²