设双曲线x^2/a^2-y^2/b^2=1
A、B点的坐标分别为A(x1,y1) ,B(-x1,-y1)
P(x,y)是双曲线上上任意一点,
x^2/a^2-y^2/b^2=1
x1^2/a^2-y1^2/b^2=1
两式相减得:
b^2(x^2-x1^2)-a^2(y^2-y1^2)=0
k(PA)=(y-y1)/(x-x1)
k(PB)=(y+y1)/(x+x1)
k(PA)*k(PB)=(y^2-y1^2)/(x^2-x1^2)
=b^2/a^2
为定值
设双曲线x^2/a^2-y^2/b^2=1
A、B点的坐标分别为A(x1,y1) ,B(-x1,-y1)
P(x,y)是双曲线上上任意一点,
x^2/a^2-y^2/b^2=1
x1^2/a^2-y1^2/b^2=1
两式相减得:
b^2(x^2-x1^2)-a^2(y^2-y1^2)=0
k(PA)=(y-y1)/(x-x1)
k(PB)=(y+y1)/(x+x1)
k(PA)*k(PB)=(y^2-y1^2)/(x^2-x1^2)
=b^2/a^2
为定值