Let the hyperbola be `(x^(2))/(a^(2))-(y^(2))/(b^(2))=1`
and any double ordinate PQ be such that `P-=(a sec theta,b tan theta)`.
`therefore" "Q-=(a sec theta, -b tan theta)`
According to the question, triangle OPQ is equilateral.
`therefore" "tan30^(@)=(b tan theta)/(a sec theta)`
`rArr" "3(b^(2))/(a^(2))="cosec"^(2)theta`
`rArr" "3(e^(2)-1)="cosec"^(2)theta`
Now, `"cosec"^(2)thetage1`
`rArr" "3(e^(2)-1)ge1`
`rArr" "e^(2)ge(4)/(3)`
`rArr" "ege(2)/(sqrt3)`