Eccentricity of ellipse?

The tangent at a point P (aCos@ , bCos@) of an ellipse x^2/a^2 + y^2/b^2 =1 ,meets the auxiliary circle in two points , the chord joining which subtends a right angle at the centre .Show that the eccentricity of the ellipse is (1 + sin^2 @ )^ -0.5