a=2,c=√2,b=√2
Z:x^2/4+y^2/2=1
y=kx+b,b不=0
(1+2K^2)x^2+4kbx+2b^2-4=0
x1+x2=-4kb/(1+2k^2)
x1x2=(2b^2-4)/(1+2k^2)
KPQ^2=KOP*KOQ
k^2=y1y2/(x1x2)=(k^2x1x2+kb(x1+x2)+b^2)/(x1x2)=k^2+(kb(x1+x2)+b^2)/(x1x2)
kb(x1+x2)+b^2=0
-4k^2b^2/(1+2k^2) +b^2=0
1+2k^2=4k^2
k^2=1/2
k=√2/2,或-√2/2