将y=k(x+1)代入y^2=-x,设A（X1,y1）,B(X2,y2)易得X1+X2=-(2k^2+1)/k^2，X1*X2=1y1*y2=k^2(X1+1)(X2+1)=-10A斜率K1为y1/X1,0B斜率K2为y2/X2,所以K1*K2=-1得证
