Question

已知圆的方程x^2+y^2-2kx-4y+2k平方=0

Answer 1

(x-k)^2+(y-2)^2=4-k^2

定点A(1,2)在圆外,则有(1-k)^2+(2-2)^2>4-k^2

1-2k+k^2>4-k^2

2k^2-2k-3>0

k^2-k>3/2

(k-1/2)^2>3/2+1/4=7/4

k-1/2>根号7/2或k-1/21/2+根号7/2或k