If tan θ1 tan θ2=−a2b2, then the chord joining two points θ1 & θ2 on the ellipse x2a2+y2b2=1 will subtend a right angle at
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: