✔ 最佳答案
1) C1: x^2+y^2-4y-3=0
C2: x^2+y^2-4x-2y-5=0
Common chord: ( C1 - C2 )
x^2 + y^2 - 4y - 3 - x^2 - y^2 + 4x + 2y + 5 = 0
2x - y + 1 = 0
2) Family of circle:
x^2 + y^2 + 4x - 2y - 1 + k ( x - 2y ) = 0 where k is real
Rearranging,
x^2 + y^2 + ( k + 4 )x + ( - 2 - 2k )y - 1 = 0
The centre: [ -(k+4)/2, (k+1)]
So,
k + 1 = 0
k = -1
Then,
x^2 + y^2 + ( -1 + 4 )x + ( - 2 + 2 )y - 1 = 0
x^2 + y^2 + 3x - 1 = 0
3) The centre of x^2+y^2+2x-8y+8=0: ( -1 . 4 )
The radius: (1/2)[sqr36] = 3
The centre of x^2+^2-6x-2y+6=0: ( 3 , 1 )
The radius: (1/2)[sqr16] = 2
The distance between radius: 3 + 2 = 5
The distance between centres: sqr [ ( - 1 - 3 )^2 + ( 4 - 1 )^2 ] = 5
So the circles touch each other externally.
Common tangent:
x^2 + y^2 - 6x - 2y + 6 - x^2 - y^2 - 2x + 8y - 8 = 0
4x - 3y + 1 = 0