a-maths!!!!!!!

a) 圓族之方程 : 2x²+2y²+2x+2y-13 + k(x+5y-10) = 0
2x²+2y²+(2+k)x+(2+5k)y-(13+10k) = 0
b) 圓心P的坐標 = [-(2+k)/2, -(2+5k)/2]
x = -(2+k)/2 ...... (1)
y = -(2+5k)/2 .....(2)
結合(1)(2)兩式以消去k
由(1),
x = -(2+k)/2
2x = -2-k
k = -2x-2 .....(3)
由(2),
y = -(2+5k)/2
2y = -2-5k
2y = -2-5(-2x-2)
2y = -2+10x+10
10x-2y+8 = 0
5x - y + 4 = 0 (此為一直線)