y=kx+2
x^2/2+y^2=1
x^2+2y^2=2
x^2+(kx+2)^2=2
(1+k^2)x^2+4kx+2=0
xA+xB=-4k/(1+k^2)
xA*xB=2/(1+k^2)
(xA-xB)^2=(xA+xB)^2-4xA*xB=(8k^2-8)/(1+k^2)^2
(yA-yB)^2=k^2*(xA-xB)^2
|AB|^2=(xA-xB)^2+(yA-yB)^2=(1+k^2)*(8k^2-8)/(1+k^2)^2=(8k^2-8)/(1+k^2)
(根号下4除以2)=?
(根号下4除以2)=√(4/2)=√2
(√2)^2=(8k^2-8)/(1+k^2)
k^2=5/3
k=±√(5/3)
直线的方程:y=2±√(5/3)x