X-2Y+5=0
X2+Y2=8
(2Y-5)^2+Y^2=8
5y^2-20y+17=0
y1+y2=4 y1*y2=17/5
y1-y2=√[(y1+y2)^2-4y1*y2]
=2/5*√15
tona=k=1/2
sina=√5/5
弦AB的长=|y1-y2|/sina=2/5*√15/√5/5=2√3