Question

已知圆x^2+y^2-2mx+4y-3=0上恰有三点到直线x+y+1=0的距离是根号2,则实数m的值是

Answer 1

m = -5

圆心o坐标:（m,-2）.

设半径为r,则 r^2-m^2 = 7..(1)

设点o到直线的距离为d.则 r - d = 根号2.

即 r = |m-1|/根号2 + 根号2 .(2)

联立(1)(2),消r,分m>=1 和 m