Question

先化简再求值(x-3y)^2+(3x+y)^2-(x+5y)^2+(x-5y)^2其中x=-2,y=3

Answer 1

解：(x-3y)^2+(3x+y)^2-(x+5y)^2+(x-5y)^2
原式=x²-6xy+9y²+9x²+6xy+y²-x²-10xy-25y²+x²-10xy+15y²
=9x²-10xy+x²-10xy
=10x²-20xy
将x=-2.，y=3代入：

原式=10x²-10xy=40-20*（-2）*3=160

追问

解：(x-3y)^2+(3x+y)^2-(x+5y)^2+(x-5y)^2
=x^2-6xy=9y^2+6xy+y^2-(x^2+10xy=25y^2)+x^2-10xy+25y^2
=10x^2+10y^2-20xy
代入x=-2,y=3得
原式=40+90-20*（-2）*3
=250
这样对么

追答

不好意思，开头化简有个地方打错了，应该是25不是15
解：(x-3y)^2+(3x+y)^2-(x+5y)^2+(x-5y)^2
原式=x²-6xy+9y²+9x²+6xy+y²-x²-10xy-25y²+x²-10xy+25y²
=9x²-10xy+x²-10xy
=10x²-20xy+10y²

将x=-2.，y=3代入：
原式=10x²-10xy+10y²=40-20*（-2）*3+10*9=250

你的是对的。= =
话说，大哥你自己会做为啥要来问呢。。。。。

Answer 2

(x-3y)^2+(3x+y)^2-(x+5y)^2+(x-5y)^2
=(x-3y)^2+(y+3x)^2+(x-5y)^2-(x+5y)^2
=x^2-6xy+9y^2+x^2+6xy+9y^2+(x-5y+x+5y)(x-5y-x-5y)
=2x^2+18y^2+(2x)(-10y)
=2x^2+18y^2-20xy
=2(x^2-10xy+9y^2)
=2(x-y)(x-9y)
=2[(-2)-3][(-2)-9x3]
=2(-5)(-2-27)
=2(-5)(-29)
=290

追问

谢谢你的回答，虽然不是很对