Question Number 43919 by peter frank last updated on 17/Sep/18
$${The}\:{tangent}\:{at}\:{P}\:{to}\:{an}\:{ellipse}\:{meet}\: \\ $$$${diretrix}\:{at}\:{Q}.{prove}\:{that}\:{the}\:{line}\:{joining} \\ $$$${the}\:{corresponding}\:{focus}\:{to}\:{P}\:{and}\:{Q}\:{are}\:{perpendicular} \\ $$