tangent eqn is x/a cos q + y/b sin q = 1 now you can a point on the ellipse as (acos x , bsinx) the length from the point on the ellipse from focus will be a(1 - ecos q) find the perp dist from focus dist. = e cos q - 1/ root (cos^2q/a^2 + sin^2 /b^2) ...and on simplifying it......post being edited....... let the perp dist be z so , (b^2cos ^ 2 q + a^2 sin ^2 q ) / (e cos q - 1)^2 * b^ 2/(ab)^2 = ( b/z)^2 so b^2/z^2 = 1/a^2 { a^2(1 - e^2)cos^2 q + a^2 sin ^ 2 q } / (1 - e cos q )^2 = ( 1 - {ecos q}^ 2 )/ ( 1 - ecos q)^ 2 = 1 + ecos q / 1 - e cos q 2a / SP - 1 = 2a / a ( 1 - e cos q ) - 1 = 1 - e cos q / 1 + e cos q so b^2 / z^ 2 = 2a / SP - 1
i think this is it......
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Not all who wander are lost
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