圆心(4,-2)，过圆心与直线y=x+2垂直的方程为y+2=-(x-4)即x+y-2=0联立方程组得x=0,y=2(0,2)到圆心距离为√(4^2+4^2)=4√2所以最短切线长为√[(4√2)^2-1^2)=√31
