先化简,再求值. x(x+2y)-(x+2)^2+2x 其中x=2,y=-2分之1

问题描述:

先化简,再求值. x(x+2y)-(x+2)^2+2x 其中x=2,y=-2分之1

x(x+2y)-(x+2)^2+2x=x²+2xy-(x²+4x+4)+2x=x²+2xy-x²-4x-4+2x=2xy-2x-4=2x(y-1)-4∵x=2,y=-1/2∴原式=2×2×(-1/2-1)-4=2×2×(-3/2)-4 =-6-4=-10