1)
假设直线OP、OQ斜率K1、K2,P（X1,Y1）Q（X2,Y2）
直线x-y+2=0带入圆
2y^2-8y+m=0,y1y2=m/2
2x^2+m-8=0,x1x2=(m-8)/2
OP垂直OQ,K1*K2=-1=Y1Y2/（X1X2
X1X2+Y1Y2=0
m/2+(m-8)/2=0,
m=4
2)m=4
x^2+y^2+2x-6y+4=0,(x+1)^2+(y-3)^2=6
圆心(-1,3)半径R^2=6
圆心到直线距离D,
D=|-1-1*3+2|/√2=√2
(PQ/2)^2=R^2-D^2=4
PQ=4