过P(5,-3),倾斜角为a,且cosa=-3/5的直线交圆x方+y方=1于P1,P2两点,求PP1*PP2和P1P2弦中点坐标（用参数方
问题描述：
过P(5,-3),倾斜角为a,且cosa=-3/5的直线交圆x方+y方=1于P1,P2两点,求PP1*PP2和P1P2弦中点坐标（用参数方
P1P*PP2=t1t2=330
答
COS=0.6,所以sin=.8
设直线 L x=5-0.6T
y=-3+0.8T
代入圆得0.1t^2+10.8t+33=0
P1P*PP2=t1t2=330
中点wei（-116/25,-87/25)