(1 + tan²θ)sin²θ =

The angle of elevation of a hovering helicopter as seen from a point 45 m above a lake is 30° and the angle of depression of its reflection in the lake, as seen from the same point and at the same time, is 60°. Find the distance of the helicopter from the surface of the lake.

(1 – sin²θ)sec²θ =

(1 – cos²θ)(1 + cot²θ) =

sin(90° – θ)cosθ + cos(90° – θ) sin θ =