An ellipse has OB as semi-minor axis, \( F \) and \( F' \) its foci and the angle \( \angle \text{FBF'} \) is a right angle. Then the eccentricity of the ellipse is
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For an ellipse with a right angle between the foci and any point, the eccentricity can be found using the relation \( e = \frac{1}{\sqrt{2}} \).