If the chord joining the points α and β on the ellipse x2a2+y2b2=1 subtends a right angle at (a, 0), then tan(α2)tan(β2)=
If tan θ1. tan θ2=−a2b2 then the chord joining two points θ1 and θ2 on the ellipse x2a2+y2b2=1 will subtend a right angle at: