计算机验证:
y1=-sqrt(2*L*k*sqrt((-2*c*k^2*x)+2*c*x+c^2*k^2-c^2+L^2)-k^4*x^2+2*k^2*x^2-x^2-2*c*k^2*x+2*c*x+c^2*k^2+L^2*k^2-c^2+L^2)/(k^2-1)[x=-(c+L)/(k-1)] = y = 0
y2=sqrt(2*L*k*sqrt((-2*c*k^2*x)+2*c*x+c^2*k^2-c^2+L^2)-k^4*x^2+2*k^2*x^2-x^2-2*c*k^2*x+2*c*x+c^2*k^2+L^2*k^2-c^2+L^2)/(k^2-1)[x=(c+L)/(k+1)] = y = 0
y3=-sqrt((-2*L*k*sqrt((-2*c*k^2*x)+2*c*x+c^2*k^2-c^2+L^2))-k^4*x^2+2*k^2*x^2-x^2-2*c*k^2*x+2*c*x+c^2*k^2+L^2*k^2-c^2+L^2)/(k^2-1)[x=-(c-L)/(k-1)] = y = 0
y4=sqrt((-2*L*k*sqrt((-2*c*k^2*x)+2*c*x+c^2*k^2-c^2+L^2))-k^4*x^2+2*k^2*x^2-x^2-2*c*k^2*x+2*c*x+c^2*k^2+L^2*k^2-c^2+L^2)/(k^2-1)[x=(c-L)/(k+1)] = y = 0