x≥1,xy1y05.若实数x,y满足{x-y+1≤0,则z=2x+y的最小值为A.22x-y-2≤0,:byB.4C.5D.106.已知圆x2+y2+4ax+2ay=0与直线2x+y10=0相切,则圆的半径为A√A.5B.2C.25D.47.已知双曲线-=1(a>0,>0)的左、右焦点分别为F1,F2,过F2且斜率为-√3的直线与双曲线在第一象限的交点为A,且AF·AF2=0若a=3-1,则F2的坐标为A.(1,0)B.(3,0)C.(2,0)D.(310)8.如图,正方体ABCDABCD1中,E,F分别为A1B1,CD的中点,则异面直线DE与A1F所成的角的余弦值为BA.5 V5AB)B6.3D6fx=x2-6B