弦心距离为|2-2-5|/根号5=根号5
半弦长=2根号5
r^2=25
(x-1)^2+(y-2)^2=25
P(-4,-13)
PO^2=5^2+15^2
PO^2-r^2=15^2
切点到P距离15
15^2=(x+4)^2+(y+13)^2
(x-1)^2+(y-2)^2=25
相减得
10x+30y+180=200
x+3y=2
(1-3y)^2+(y-2)^2=25
10y^2-10y+5=25
y^2-y-2=0
x=5,y=-1
x=-4, y=2
分别联合P(-4,-13)和两切点即可
y=4x/3-23/3可化成
4x-3y-23=0
和x=-4