(2x+y)2-(2x-y)(x+y)-2(x-2y)(x+2y),其中x= ,y=-2 化简求值
问题描述:
(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
答
(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....