A(x1,y1),B(x2,y2),P(2,-3)
P是AB中点:
1)x1+x2 = 2*2即x1+x2=4
2)y1+y2 = 2*(-3)即y1+y2=-6
A,B在圆上:
3)x1^2+y1^2 = 20
4)x2^2+y2^2 = 20
3) - 4)
(x1-x2)*4 =(y2-y1) * (-6)
化简,
(y1-y2)/(x1-x2) = 4/6 = 2/3
这就是斜率2/3,点P(2,-3),利用点斜式写出直线方程
y+3 = 2/3 * (x-2)