作业帮(2x+y)2-(2x-y)(x+y)-2(x-2y)(x+2y),其中x= ,y=-2 化简求值x+y+z=4,x²+y²+z²=2,求xy+yz+zx的值
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(2x+y)2-(2x-y)(x+y)-2(x-2y)(x+2y),其中x= ,y=-2 化简求值x+y+z=4,x²+y²+z²=2,求xy+yz+zx的值
(2x+y)2-(2x-y)(x+y)-2(x-2y)(x+2y),其中x= ,y=-2 化简求值
x+y+z=4,x²+y²+z²=2,求xy+yz+zx的值
(2x+y)2-(2x-y)(x+y)-2(x-2y)(x+2y),其中x= ,y=-2 化简求值x+y+z=4,x²+y²+z²=2,求xy+yz+zx的值
（2X+Y）^2-（2X-Y）（X+Y）-2（X-2Y）（X+2Y）
解原式=4X^2+Y^2+4XY-2X^2-2XY+XY+Y^2-2(X^2-4Y^2)
=4X^2+Y^2+4XY-2X^2-2XY+XY+Y^2-2X^2+8Y^2
=4X^2-2X^2-2X^2+Y^2+Y^2+8Y^2+4XY-2XY+XY
=10Y^2+3XY
把x= ,y=-2代入就行了.
x+y+z=4,x²+y²+z²=2,求xy+yz+zx的值
(x+y+z)^2=x^2+y^2+z^2+2(xy+xz+yz)
16=2+2(xy+xz+yz)
故zx+xy+yz=7
(2x+y)2-(2x-y)(x+y)-2(x-2y)(x+2y)
=4x²+4xy+y²-(2x²+xy-y²)-2(x²-4y²)
=4x²+4xy+y²-2x²-xy+y²-2x²+8y²
=3xy+10y²
=3x*(-2)+10...
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(2x+y)2-(2x-y)(x+y)-2(x-2y)(x+2y)
=4x²+4xy+y²-(2x²+xy-y²)-2(x²-4y²)
=4x²+4xy+y²-2x²-xy+y²-2x²+8y²
=3xy+10y²
=3x*(-2)+10*4
=40-6x
不知你的x是多少，你可以自己代入计算
(x+y+z)²=4²
x²+y²+z²+2xy+2yz+2zx=16
2+2(xy+yz+zx)=16
xy+yz+zx=7
收起
x²+y²+z²+2(xy+yz+zx)=(x+y+z)² = 4² = 16
x²+y²+z²=2
2(xy+yz+zx) = 16 - 2 = 14
xy+yz+zx = 7
(x+y+z)的平方等于x2+y2+z2 +2（xy+yz+zx）=16
x2+y2+z2=2
2（xy+yz+zx)=14
xy+yz+zx=7
给分哦
原式=4x²+4xy+y²-2(x²-4y²)-(2x²+xy-y²)=3xy+10y²
然后代入数值，即为40-6x
由题知（x+y+z)²=16,展开为x²+y²+z²+2(xy+xz+yz)=16
代入数值后，xy+xz+yz=(16-2)/2=7
7