y-1=k(x-1)
y=kx+(1-k)
代入2x²-y²=2
(2-k²)x²-2k(1-k)x-(1-k)²-2=0
P是中点则(x1+x2)/2=1
所以x1+x2=2k(1-k)/(2-k²)=2
k-k²=2-k²
可以