Given equation of ellipse is 9x2+3y2=1
Normal at (3cosθ,3sinθ) is
3secθ.x−3cosecθy=6
⇒Slope m1=3cosecθ3secθ=3tanθ
Normal at (−3sinθ,3cosθ)
−3cosecθ.x−3secθ.y=6
⇒Slope m2=3secθ−3cosecθ=−3cotθ
Angle between normal is β.
⇒tanβ=∣1+m1m2m1−m2∣=∣1−33tanθ+3cotθ∣=∣2sinθcosθ3∣
⇒tanβ=sin2θ3⇒sin2θ2cotβ=32