Question

已知过点m(-3.-3)的直线与直线l与圆x2+y2+4y-21=0交与ab两点 若ab长为2根号15求l方程

Answer 1

C:x^2+y^2+4y-21=0

C(0,-2),r=5

L:y+3=k(x+3)

kx-y-3+3k=0

h=|2-3+3k|/√(1+k^2)

h^2=r^2-(AB/2)^2

(3k-1)^2/(1+k^2)=5^2-(2√15/2)^2

k=-3

L:3x+y+9=0